Approximately 1 percent of the total solar energy reaching the earth is fixed by photosynthesis.
Photosynthesis is the process by which green plants and some other organisms convert light energy into chemical energy, which can be stored in the form of organic compounds such as glucose. This process occurs in the chloroplasts of plant cells and requires sunlight, water, and carbon dioxide. However, not all of the solar energy that reaches the earth is available for photosynthesis because some of it is reflected or absorbed by the atmosphere and the earth's surface. Therefore, only a small fraction of the total solar energy is actually used by plants for photosynthesis.
In conclusion, only about 1 percent of the total solar energy reaching the earth is fixed by photosynthesis due to the limitations of this process and the amount of available sunlight.
To know more about photosynthesis, visit:
https://brainly.com/question/29764662
#SPJ11
how does chronic stress affect your brain's size
Chronic stress can lead to a decrease in the size of certain brain regions, such as the prefrontal cortex and hippocampus.
Chronic stress can have detrimental effects on the brain's structure and function. One key mechanism through which this occurs is the prolonged exposure to stress hormones, particularly cortisol. High levels of cortisol can damage and shrink certain brain regions.
The prefrontal cortex is responsible for executive functions such as decision-making and emotional regulation, while the hippocampus plays a crucial role in memory formation and learning. Studies have shown that chronic stress can reduce the volume and impair the connectivity of these regions.For example, a study published in the journal Nature Neuroscience in 2014 examined the effects of chronic stress on the brain. The researchers exposed rats to chronic stress for several weeks and found a significant decrease in the volume of the prefrontal cortex and hippocampus compared to non-stressed rats.
Chronic stress can have a negative impact on the size of specific brain regions. The prefrontal cortex and hippocampus are particularly vulnerable, and their shrinkage can contribute to cognitive and emotional difficulties associated with chronic stress. However, it's worth noting that the brain is a complex organ, and the effects of chronic stress can vary among individuals. Proper stress management techniques and seeking support can help mitigate the potential impact on brain structure and function.
To know more about brain visit:
https://brainly.com/question/1247675
#SPJ11
The technique used for DNA amplification is:
Select one:
a. Polymerase chain reaction b. PRIMER 3
c. BLAST
d. Gel electrophoresis
a. Polymerase chain reaction (PCR) is the technique used for DNA amplification. PCR is a method used to amplify a specific DNA sequence, generating millions or billions of copies of that sequence.
This technique involves the use of DNA polymerase enzyme, primers, and nucleotides to selectively amplify the DNA of interest through a series of heating and cooling cycles.
The technique of DNA amplification refers to the process of making multiple copies of a specific DNA sequence, which can then be analyzed and studied in various ways. Polymerase chain reaction (PCR) is the most commonly used method for DNA amplification. PCR involves using a special type of enzyme called a DNA polymerase to repeatedly replicate a specific DNA sequence in a test tube. The process involves repeated cycles of heating and cooling the reaction mixture to allow the DNA strands to separate and then rejoin with the primers and the DNA polymerase to form new copies. This results in an exponential increase in the number of copies of the targeted DNA sequence, which can then be detected and analyzed using various techniques such as gel electrophoresis, DNA sequencing, and hybridization. PCR has revolutionized many areas of molecular biology and genetics research, as it allows for the rapid and accurate amplification of specific DNA fragments, even from very small amounts of starting material.
To know more about DNA
brainly.com/question/30006059
#SPJ11
the cornea belongs to the tunica fibrosa (fibrous layer) of the eyeball.
T/F
The cornea belongs to the tunica externa (external layer) of the eyeball, not the tunica fibrosa (fibrous layer). The tunica fibrosa includes the sclera, which is the white, tough outer layer of the eyeball.
The cornea, on the other hand, is a transparent, dome-shaped structure located at the front of the eye. It is part of the tunica externa and serves as the clear window that allows light to enter the eye. Composed primarily of collagen fibers, the cornea provides structural support and helps to focus light onto the retina at the back of the eye, enabling vision.
Learn more about cornea here:
https://brainly.com/question/29366850
#SPJ11
list of any 6 importance of environmental science
The 6 importance of environmental science are:
Conservation and PreservationSustainable DevelopmentClimate ChangeBiodiversityPollution ControlHuman HealthWhat are importance of environmental science?Environmental science aids resource understanding, conservation, and preservation for future generations. Utilize resources sustainably to avoid harm to the planet.
Environmental science explains biodiversity and species' roles in ecosystems. Environmental science aids in protection of endangered species and controlling pollution. It aids development of pollution control measures to minimize impact on environment & understand impact of enviro factors on human health.
Learn more about environmental science from
https://brainly.com/question/3443105
#SPJ1
Which of the following structures appears as a large bulge just rostral to the medulla? A. Pons B. Midbrain C. Cerebellum D. Medulla oblongata. E. Hypothalamus.
The structure that appears as a large bulge just rostral to the medulla is the pons, which is part of the brainstem. It is located between the medulla oblongata and the midbrain. The pons is involved in several important functions, including controlling breathing, sleep, and sensory information. It also serves as a relay center for messages that travel between different parts of the brain and spinal cord.
The pons contains many different nerve fibers and nuclei that are important for motor and sensory functions. The main motor pathway that passes through the pons is the corticospinal tract, which helps to control voluntary movements. The pons also contains several cranial nerve nuclei, including those that control eye movements and facial expressions.
To know more about medulla click this link -
brainly.com/question/30771321
#SPJ11
an endemic family of frogs is found on a series of oceanic islands formed by
An endemic family of frogs refers to a group of frog species that are unique to a specific geographic region, in this case, a series of oceanic islands.
An endemic family of frogs refers to a group of frog species that are unique to a specific geographic region, in this case, a series of oceanic islands. Oceanic islands are landmasses formed by geological processes such as volcanic activity, tectonic movements, or coral growth, and they are located in the middle of vast oceanic expanses.
The presence of an endemic frog family on these oceanic islands indicates that these amphibians have evolved and adapted to the specific ecological conditions of the islands. This unique development may have resulted from the frogs' isolation from other mainland populations, leading to the diversification of species over time.
Island ecosystems, including those found on oceanic islands, are known for their high rates of endemism. The isolation of these habitats fosters unique evolutionary paths, creating new species that are specifically adapted to their island environments. As a result, these islands serve as biodiversity hotspots and provide valuable insights into evolutionary processes and species conservation.
To know more about oceanic islands visit: https://brainly.com/question/28283590
#SPJ11
what portion of the eye controls how much light passes into the posterior chamber?
The portion of the eye that controls how much light passes into the posterior chamber is the iris. The iris is a colored ring-shaped structure that lies behind the cornea and in front of the lens. It contains a circular muscle that can constrict or dilate the pupil, which is the opening in the center of the iris.
The size of the pupil controls the amount of light that enters the eye, with a smaller pupil allowing less light and a larger pupil allowing more light. Therefore, the iris plays a crucial role in regulating the amount of light that reaches the posterior chamber of the eye.
When the light intensity is high, the sphincter pupillae contracts, causing the pupil to constrict and reduce the amount of light entering the eye. Conversely, in low light conditions, the dilator pupillae contracts, enlarging the pupil and allowing more light to enter. This process of adjusting the pupil size helps maintain optimal light levels in the posterior chamber, protecting the retina and ensuring proper vision.
To know more about posterior chamber visit:-
https://brainly.com/question/29899206
#SPJ11
What is the purpose of the serous fluid that is located between visceral and parietal serosa?
a) It allows organs to slide with little friction against each other and against the cavity walls.
b) directional terminology refers tothe body in the position
c) it is limited because it cannot produce sharp images of structures within cells
d) pharyngeal pouches, dorsal hollow nerve cord, and segmentation
The purpose of the serous fluid that is located between visceral and parietal serosa is to allow organs to slide with little friction against each other and against the cavity walls. This fluid acts as a lubricant, reducing friction and allowing smooth movements of organs. It also helps to cushion and protect the organs.
Serous fluid, also known as serosal fluid, is any benign bodily fluid that, in physiology, resembles serum and is often translucent or pale yellow in colour. The liquid fills bodily cavities on the inside. Serous glands produce secretions that are loaded with water and proteins to form serous fluid.
To know more about serous fluid
https://brainly.com/question/30783380
#SPJ11
sensitive tissue in the right atrium wall that initiates the heartbeat is known as the
The sensitive tissue in the right atrium wall that initiates the heartbeat is known as the sinoatrial node (SA node).
This small, specialized group of cells acts as the natural pacemaker of the heart, generating electrical impulses that cause the heart muscle to contract and pump blood throughout the body. The SA node is located in the upper part of the right atrium and is responsible for setting the heart rate and rhythm. When functioning properly, the SA node coordinates the contraction of the atria and ventricles, ensuring that blood flows efficiently through the circulatory system. Dysfunction of the SA node can lead to arrhythmias and other heart problems.
Hello! The sensitive tissue in the right atrium wall that initiates the heartbeat is known as the sinoatrial (SA) node. The SA node is often referred to as the heart's natural pacemaker, as it generates electrical impulses that spread throughout the heart muscles, prompting them to contract and pump blood. This vital process ensures a consistent, rhythmic heartbeat necessary for maintaining proper circulation and overall cardiovascular health.
To know about heartbeat:
https://brainly.com/question/30870831
#SPJ11
3. How are the following adapted to their functions? a) Lens (2 marks) b) Choroid (2 marks)
Answer:
The lens focuses the light on the retina. This is achieved by the ciliary muscles in the eye changing the shape of the lens, bending or flattening it to focus the light rays on the retina. This adjustment in the lens, known as accommodation, is necessary for bringing near and far objects into focus.
Choroid- It is dark pigmented and membranous layer that prevents light reflection witan eye to pre vent distortion of the image; it has blood vessels that nourishes the eye, supply oxygen and removal of waste product.
if a population starts with 50 cells and the population is allowed to grow for 5 generations, what is the final population size
If a population starts with 50 cells and grows for 5 generations, assuming that each cell divides once per generation, the final population size can be of 1600 cells.
Assuming that each cell produces 2 offspring and there is no cell death, the final population size would be 1600 cells. This is because each generation doubles the population size, so after 5 generations, the population would have doubled 5 times (2^5 = 32) and the initial population size of 50 would be multiplied by 32, resulting in a final population size calculated using the formula:
Initial population size * 2^number of generations
In this case:
50 cells * 2^5 generations = 50 * 32 = 1600 cells
So, the final population size would be 1600 cells.
To know more about population size visit:
https://brainly.com/question/30881076
#SPJ11
what is the procedure performed to gain access to the airway below a tracheal obstruction?
The procedure performed to gain access to the airway below a tracheal obstruction is called a tracheostomy.
A tracheostomy is a surgical procedure that involves creating an opening (stoma) in the front of the neck and into the trachea (windpipe). This procedure is performed when there is a blockage or obstruction in the upper airway, such as a severe tracheal or laryngeal obstruction, that prevents adequate airflow into the lungs. By creating a new airway opening below the obstruction, a tracheostomy allows for direct access to the lower respiratory tract and facilitates the passage of air into the lungs.
During a tracheostomy, a small incision is made in the neck, and a tube or tracheostomy cannula is inserted into the trachea. The cannula is connected to a ventilation device or respiratory support system to assist with breathing. The procedure is typically performed under sterile conditions and may be temporary or permanent, depending on the underlying condition or need for airway management.
A tracheostomy is the procedure performed to establish a new airway opening below a tracheal obstruction. It provides an alternative route for air to enter the lungs and ensures adequate ventilation when the upper airway is compromised. Tracheostomies are essential in situations where immediate access to the lower airway is required for effective respiration and can be life-saving in emergency situations.
Learn about tracheal here:
https://brainly.com/question/2948062
#SPJ11
the amount of food energy converted into biomass by consumers is called secondary production. group of answer choices true false
True. The statement is true. Secondary production refers to the amount of food energy that is converted into biomass by consumers in an ecosystem.
This includes all the organisms that consume producers (herbivores) as well as other consumers (carnivores, omnivores). Secondary production is an important ecological concept that helps us understand how energy flows through an ecosystem.
The amount of food energy converted into biomass by consumers is called secondary production. Your main answer is: True.
Secondary production refers to the process by which consumers (herbivores and carnivores) convert the energy obtained from consuming primary producers (plants) or other consumers into new biomass. This energy conversion contributes to the overall productivity and functioning of an ecosystem.
To know more about ecosystem , click here
https://brainly.com/question/31459119
#SPJ11
by manipulating a single gene, scientists have been able to control sexual orientation in
There is currently no scientific evidence to suggest that sexual orientation can be controlled or manipulated through the manipulation of a single gene. Sexual orientation is believed to be influenced by a combination of genetic, environmental, and societal factors.
While certain genes have been identified as potentially playing a role in sexual orientation, research in this area is still in its early stages and the complexity of human sexuality makes it difficult to pinpoint a single genetic factor that can determine sexual orientation.
Furthermore, attempting to control or manipulate sexual orientation through gene manipulation raises ethical concerns and goes against the principle of respecting individual autonomy and diversity. Therefore, it is important to approach the topic of sexual orientation with sensitivity and understanding and to support the rights of individuals to express their sexual orientation freely and without discrimination.
You can learn more about genes at: brainly.com/question/31121266
#SPJ11
which muscle is a powerful agonist of adduction and medial rotation of the arm?
The muscle that is a powerful agonist of adduction and medial rotation of the arm is the pectoralis major muscle. This muscle is located in the chest area and is responsible for moving the arm inwards towards the body, as well as rotating it towards the center of the body.
The pectoralis major muscle is commonly used in exercises such as bench presses and push-ups, and is a vital muscle for upper body strength and mobility. It is important to train this muscle to maintain proper posture and prevent shoulder injuries, especially in activities that involve a lot of overhead lifting or throwing motions.
The muscle that serves as a powerful agonist of adduction and medial rotation of the arm is the latissimus dorsi. This large, flat muscle is located in the back, extending from the lower spine to the upper arm bone (humerus). As an agonist, it plays a primary role in performing the mentioned movements, working with other muscles in the shoulder and upper back region. Its actions help stabilize the shoulder joint and facilitate various activities, such as rowing, swimming, or pulling motions. In summary, the latissimus dorsi is essential for adduction and medial rotation of the arm.
To know about agonist:
https://brainly.com/question/30386211
#SPJ11
The _____ consists of an inner mass of cells that will eventually develop into the embryo.
A. blastocyst
B. trophoblast
C. endoblast
D. cytocyst
The blastocyst consists of an inner mass of cells that will eventually develop into the embryo. The answer is A.
During early embryonic development, the fertilized egg undergoes a series of cell divisions to form a hollow ball of cells called a blastocyst. The blastocyst consists of two main cell populations: the inner cell mass and the trophoblast.
The inner cell mass is a cluster of cells located at one end of the blastocyst and is the group of cells that will eventually differentiate and develop into the embryo. The trophoblast is a layer of cells that surrounds the inner cell mass and is responsible for implanting the blastocyst into the uterine wall and forming the placenta.
The endoblast and cytocyst are not correct terms used to describe structures in the early embryo. Hence, the correct option is A.
To know more about embryonic development, refer here:
https://brainly.com/question/31856021#
#SPJ11
.com, .net, and .edu are all examples of what level of the dns naming hierarchy?
The ".com", ".net", and ".edu" are all examples of top-level domains (TLDs) in the DNS naming hierarchy.
The DNS (Domain Name System) hierarchy is a structured system for organizing domain names. TLDs are the highest level in this hierarchy and are located to the right of the last dot in a domain name. They represent the highest level of categorization for domain names and help to organize and classify websites on the Internet.
Other examples of TLDs include .org, .gov, .mil, .int, and country-specific TLDs like .uk, .fr, or .jp. TLDs are managed by the Internet Assigned Numbers Authority (IANA).
To learn more about DNS:
https://brainly.com/question/27960126
#SPJ11
which kind of organic macromolecule does not have a single kind of monomer subunit?
Lipids are a type of organic macromolecule that does not have a single kind of monomer subunit.
Lipids are a diverse group of molecules that are insoluble in water but soluble in organic solvents such as ethanol or chloroform. Unlike proteins (composed of amino acids), nucleic acids (composed of nucleotides), and carbohydrates (composed of monosaccharides), lipids do not have a specific single monomer subunit that defines their structure. Instead, lipids are composed of various building blocks or subunits, which can include fatty acids, glycerol, and other components. These building blocks can combine in different ways to form different types of lipids, such as triglycerides, phospholipids, and sterols. The diverse nature of lipids and their lack of a singular monomer subunit make them distinct from other organic macromolecules.
Learn more about organic macromolecule here:
https://brainly.com/question/31856446
#SPJ11
why does adding radials to a 1/4 vertical antenna seem to increase the swr
The adding radials to a 1/4 wavelength vertical antenna should not increase the SWR, but rather decrease it, as long as the radials are the proper length and installed correctly.
Adding radials to a 1/4 wavelength vertical antenna should not increase the SWR (standing wave ratio), but instead, it should decrease it. The radials help to improve the antenna's ground plane, which in turn helps to increase the antenna's efficiency and reduce the SWR.
However, it is possible that adding radials to a 1/4 wavelength vertical antenna could cause an increase in SWR if the length of the radials is not tuned properly. The length of the radials should be approximately 1/4 wavelength long, and they should be installed at the same height as the base of the vertical element.
If the radials are not the proper length or are not installed correctly, they can affect the antenna's radiation pattern and cause a mismatch between the antenna and the transmission line, which can result in an increase in SWR.
To know more about vertical antenna here
https://brainly.com/question/27963865
#SPJ4
higher intakes of all of the following except ______ are associated with increased bone mass.
Answer: Sodium
Explanation: Higher intakes of all of the following except sodium are associated with increased bone mass.
which explains why an offspring having white flowers results from this cross of blue-flowered parents?
The probability of an offspring expressing a blue flower phenotype is 2/3 or approximately 66.7%.
The probability that an offspring of this cross expresses plants with blue flower phenotypes can be determined using Punnett square analysis.
In this case, the cross is between two heterozygous plants (Pp). When the alleles are crossed, the possible genotypes of the offspring are PP, Pp, and pp. Out of these three genotypes, the PP and Pp genotypes both result in the expression of blue flower phenotypes. Only the pp genotype would result in a white flower phenotype.
Since there are two genotypes (PP and Pp) that express purple flower phenotypes out of the three possible genotypes, the probability of an offspring expressing a blue flower phenotype is 2/3 or approximately 66.7%.
To learn more about phenotype follow the link:
https://brainly.com/question/32129453
#SPJ4
The complete question is:
In a cross of blue-flowered heterozygous plants (Bb), the letter B represents the allele for blue flowers and the letter b represents the allele for white flowers.
What is the probability that an offspring of this cross expresses plants with blue flower phenotypes?
which genes are encoding for subunits of nitrogenase, the main enzyme for nitrogen fixation?
The genes encoding for the subunits of nitrogenase, the main enzyme for nitrogen fixation, are nif genes.
These genes are typically found in clusters in various bacterial species, including those capable of nitrogen fixation. In general, the nif genes code for the various subunits of nitrogenase, including the two structural subunits, α and β, and other proteins necessary for nitrogen fixation, such as those involved in the biosynthesis of cofactors or the regulation of the process.
The expression of these genes is tightly regulated to ensure that nitrogen fixation only occurs when necessary, as it is an energy-intensive process. In addition, the expression of these genes can be inhibited under certain environmental conditions, such as high oxygen concentrations.
To learn more about nitrogen fixation here
https://brainly.com/question/4191267
#SPJ4
What will happen if primer has variable site at 3' end?
If a primer has a variable site at the 3' end, it may not efficiently bind to the template DNA during PCR amplification, leading to incomplete or incorrect amplification.
this is that the 3' end of the primer is the most crucial region for binding to the template DNA during PCR amplification. This region must be complementary to the target DNA sequence to allow for efficient annealing and extension by the DNA polymerase. If the 3' end of the primer contains a variable site, there is a risk that it may not be complementary to the template DNA, resulting in weak or incorrect binding. This can lead to amplification failure or the production of non-specific PCR products. Therefore, it is important to design primers with a stable and specific 3' end to ensure successful PCR amplification.
To know more about PCR amplification, , click here
https://brainly.com/question/30880827
#SPJ11
100 miles per hour upside down and sideways
The statement "100 miles per hour upside down and sideways" implies a velocity of 100 miles per hour in both the upside-down and sideways directions.
Velocity is a vector quantity that includes both magnitude (speed) and direction. In this statement, the magnitude of velocity is given as 100 miles per hour. However, the phrase "upside down and sideways" does not provide a specific direction in a conventional sense. It is unclear whether it refers to motion in multiple directions simultaneously or to unconventional orientations.
If we assume that the intended meaning is simultaneous motion in two perpendicular directions, such as upside down and sideways, we would need to use vector addition to calculate the resultant velocity. In this case, the magnitude of the resultant velocity would be the square root of the sum of the squares of the individual velocities in each direction.
However, it is important to note that the statement lacks specific information regarding the angles or axes of motion, making it challenging to perform an accurate calculation.
The statement "100 miles per hour upside down and sideways" suggests a velocity of 100 miles per hour in unconventional orientations. While the concept of velocity can be understood, the lack of specific information regarding the directions and angles involved makes it difficult to provide a precise calculation or interpretation.
To know more about velocity ,visit:
https://brainly.com/question/80295
#SPJ11
An open sore in the stomach wall due mainly to the action of a bacterium,Helicobacter pylori,is
A)pernicious anemia.
B)heartburn.
C)a hiatal hernia.
D)an ulcer.
the lymphoid tissue of the spleen ("white pulp") contains many __________.
The lymphoid tissue of the spleen ("white pulp") contains many lymphocytes.
The spleen is a lymphatic organ that filters the blood and plays a critical role in the immune response. It is divided into two main types of tissue: the red pulp and the white pulp.
The white pulp is a region of the spleen where lymphocytes and other immune cells are concentrated and is responsible for mounting an immune response against blood-borne pathogens. The lymphoid tissue of the spleen's white pulp contains a high density of lymphocytes, including both B and T cells, which are important for recognizing and fighting infections.
Additionally, the white pulp also contains other immune cells such as macrophages and dendritic cells that are involved in presenting antigens to the lymphocytes and helping to activate an immune response.
To know more about lymphoid tissue, refer here:
https://brainly.com/question/4266699#
#SPJ11
a polarized electrical receptacle may be identified by
A polarized electrical receptacle can be identified by the presence of one vertical slot that is larger than the other.
The larger slot is intended to be used for the neutral wire, while the smaller slot is for the hot wire. This design ensures that the electrical device being plugged in is connected to the correct polarity, which is important for safety and proper operation of the device.
It is important to note that not all electrical devices require a polarized plug, but if a device has one, it should be used with a polarized receptacle.
To know more about electrical receptacle click on below link :
https://brainly.com/question/31240733#
#SPJ11
a varico/cele is the __________ of the veins in the scrotum (male pouch).
A varicocele is a medical condition characterized by the enlargement of the veins within the scrotum, the pouch of skin that contains the testes in males. Varicoceles are caused by the weakening of the valves within the veins, which normally prevent blood from flowing backward. This causes blood to pool in the veins, leading to their enlargement and the resulting varicocele.
Varicoceles are more common on the left side of the scrotum, but can occur on both sides. They may be asymptomatic or can cause pain, swelling, and discomfort in the affected area. Varicoceles may also interfere with normal testicular function, leading to reduced fertility or testicular atrophy.
Varicoceles are typically diagnosed through a physical exam or imaging tests such as ultrasound. Treatment may include medication, surgery, or simply monitoring the condition. In some cases, varicoceles may not require treatment, particularly if they are not causing any symptoms or complications.
To know more about varicocele click here:
https://brainly.com/question/29911053
#SPJ11
the three basic ingredients of cordials are botanicals, sweeteners and spirits. select an answer and submit. for keyboard navigation, use the up/down arrow keys to select an answer. a true b false
The statement "The three basic ingredients of cordials are botanicals, sweeteners and spirits" is: A. True.
Cordials are alcoholic beverages that are typically made by mixing spirits with sweeteners and flavoring agents, which can include botanicals such as herbs, spices, and fruits. The combination of these three ingredients creates a sweet, flavorful drink that can be served on its own or used as a component in mixed drinks and cocktails. Botanicals are an important ingredient in many cordials, as they add unique flavor profiles and aromas. Some common examples of cordials include triple sec, amaretto, and Irish cream. Therefore, the statement that the three basic ingredients of cordials are botanicals, sweeteners, and spirits is true.
Learn more about Cordials here:
https://brainly.com/question/31908463
#SPJ11
2. By what time period was all milk pasteurized in the United States?
Answer:
In 1987,
the Food and Drug Administration (FDA) issued its final regulation on the mandatory pasteurization of all milk or milk products (with the exception of some cheeses) for sale or distribution in interstate commerce.
Answer:1895
Explanation:
In 1895, commercial pasteurizing machines for milk were introduced in the United States. "By 1917, pasteurization of all milk except that from cows proven to be free of tuberculosis was either required or officially encouraged in 46 of the country's 52 largest cities
