One such experiment has been designed by Robert Lawrence, a physician at Kings County Hospital in New York City, and Henry Soloway, a student at the State University of New York College of Medicine. They write:

"The human body can be likened to an engine. Structures such as the heart, lungs and kidneys are essential to its operation. If any of these organ systems breaks down, the engine stops. Other structures control the rate at which the engine operates; they are analogous to the flywheel, governor and throttle. These include the endocrine-gland complex, comprised of such organs as the pituitary, thyroid, adrenals, pancreas and gonads.

"The product of certain of these glands, such as the adrenals or the pancreas, is essential to life. Their destruction by injury or disease leads to death unless the missing hormones are supplied to the body artificially. The destruction of others, such as the thyroid or gonads, need not result in death, but depriving an animal of them can seriously alter various body structures and functions such as skin texture and color, the growth and distribution of hair, the sex drive, the rate at which the organism grows, and so on.

"Unlike other glands, those of the endocrine complex elaborate and liberate chemical substances directly into the bloodstream. Known as hormones, these substances include insulin, estrogen, cortisone, testosterone and thyroxin Once secreted into the circulation they act throughout the body to control the rates of its various processes.

"Obviously the glands can function at three levels: optimal production, overproduction and underproduction. The experiment we shall describe is designed to demonstrate the reaction in a group of experimental animals when the thyroid gland is made to function at each of these three levels.

"The thyroid gland is located just below the Adam's apple. It elaborates the iodine-containing hormone thyroxin, which helps to control the animal's rate of metabolism. Our experiment employs the dried and powdered thyroid gland, which contains active thyroid hormone. The preparation may be purchased from the General Biological Supply House of 5200 South Hoyne Avenue in Chicago. A 10-gram bottle, sufficient for this experiment, is priced at 95 cents.

"In addition to thyroxin, the experiment requires a second compound: 6-npropyl 2-thiouracil, usually called PTU. When administered in sufficient quantity, this compound will render the thyroid gland almost completely incapable of producing thyroxin. By using either of the two preparations it is possible to inhibit the action of the experimental animal's thyroid and so reduce its natural supply of thyroxin far below the optimal level. Then, by administering the thyroid powder, one can raise the thyroxin level to any desired amount. The animal is physiologically unable to distinguish between thyroxin produced by its own thyroid gland and that administered to it. This so-called inhibition-replacement technique enables the experimenter to observe the broad spectrum of effects that accompanies variations in the activity of the thyroid gland. The amount of thyroxin needed to restore normal function in an animal with a nonfunctioning thyroid gland will be measured, and records will be made of how the various levels of simulated thyroid activity modify the body's responses to certain abnormal physiological states.

"The experiment requires 20 male albino rats, each weighing between 45 and 50 grams. These can be procured either through firms specializing in biological supplies or from pet stores. It is inadvisable to mix male and female rats in the experiment. The use of females rather than males also complicates the experiment, because the hormones involved in the ovarian cycle interact with other hormones in a regular manner that tends to make the analysis of the experiment difficult. It is also inadvisable to perform the experiment with guinea pigs, because in these animals the thyroid normally functions at a very low level.

"The experimental rats should be divided into four groups of five each. The individuals in each group should be selected so that their weights are as similar as possible. The groups are placed in four cages, which should be approximately 12 inches high, 12 inches wide and 18 inches long. All-metal construction is recommended, but wooden frames covered with half-inch wire mesh are satisfactory. The cages should be equipped with floors of wire mesh so that urine and feces can fall through the wire into a shallow pan.

"The reliability of the experimental results will depend heavily on how the animals are maintained during the period of the experiment. The cages must be kept scrupulously clean and out of drafts. Laboratory rats are more susceptible to disease than their untamed cousins.

"When a rat is in a cold environment, its nervous system senses the loss of heat and communicates the need for energy to the thyroid. The gland thereupon liberates additional thyroxin, which in turn increases the rate at which food is 'burned.' Since the objective of the experiment is to observe the effects that accompany various levels of thyroxin in the blood independent of environmental factors, the room housing the rats must be maintained at a uniform temperature. If possible, the temperature should be held within the range of 69 to 72 degrees Fahrenheit. The animals should be exposed to natural daylight occasionally, but the cages must be protected from direct sunlight because the eyes of albino rats contain little pigment and are easily injured by strong light.

"Each cage should be equipped with a water-dispenser. An automatic dispenser can be made from a pint bottle, an elbow of glass tubing, a short length of rubber tubing and a rubber stopper perforated with a hole the same diameter as the rubber tubing. The end of the glass elbow is inserted into the tubing, which is pushed through the hole in the stopper. The stoppered bottle is filled and upended so that a small air space remains at the top, and is mounted so that the glass tube is vertical inside the cage. It is advisable to polish the exposed end of the tube in a gas flame t prevent the rats from cutting them selves.

"PTU can be obtained from the Lederle Laboratories in Pearl River N. Y. A bottle containing 100 five gram tablets is priced at $2.61. Amateurs can purchase the substance, how ever, only through a recognized scientific institution, school or board of education.

"PTU is administered in the drinking water. The required .02-per-cent solution is made by dissolving .4 gram of PTU (eight tablets) in two quarts of boiling water. (PTU does not dissolve readily in cold water.) After cooling, the solution may be stored in a stoppered bottle from which the water bottles are replenished as required. One group of rats, which is reserved as a control, receives plain tap-water. The other three groups receive the PTU solution.

"The dried-thyroid powder containing the hormone is administered with the rat's food. From the strictly scientific point of view this technique leaves something to be desired, because it is impossible to control the dosage accurately. One can predict neither the precise quantity of food that will be eaten nor the amount of thyroxin absorbed from the digestive tract. Ideally an accurately measured solution containing the pure hormone would be injected under the skin. Pure thyroxin is costly, however, and injection is inconvenient. In this experiment it is permissible to sacrifice some accuracy for a gain in convenience.

"Each of the four experimental groups receives a diet that varies only in its concentration of thyroid powder. A standard ration is stocked by most biological supply-houses and is relatively I inexpensive. Most experimenters prefer to work with the prepared food unless a diet is required that is deficient in some particular element. For those who prefer to make up their own rat food, the accompanying recipe is recommended [see table above].

"Because the object of the experiment . is to show the effects of normal, high and low thyroid activity, two groups of rats receive the stock ration to which no thyroid powder is added. One of these is the control group. It receives plain food and water. The second is the group to be deprived of thyroxin. It receives PTU and plain food. The remaining two groups receive medication in both food and water. The first receives PTU and just enough thyroxin to restore its normal complement of the hormone. It has been calculated that the addition of three parts of thyroid powder to 1,000 parts of stock ration almost exactly replaces the amount of thyroxin that would be liberated naturally. If all goes well, the biological functioning of this group should closely match that of the control group. The fourth group will simulate the effects of an overactive thyroid. Excessive thyroxin is administered: 12 parts of thyroid powder to 1,000 parts of stock ration.

"The prescribed diets should be prepared in bulk and stored in appropriately labeled boxes from which individual food dishes are filled as required. A 50-gram rat will consume on the average about seven grams of food per day. The food dishes should be about two inches high and should have steep sides to prevent spillage. They should be anchored to the floors of the cages and kept filled, because the capacity of a rat's stomach is small. Consequently the animals will eat almost continuously.

"The experiment gets under way as soon as the rats have been placed in their cages and supplied with medicated food and water. Each animal should have been marked for identification either by an ear punch or a dye and listed on an individual record sheet with column headings for body length, weight, oxygen consumption and general comments, including a description of hair condition.

"Carbon dioxide is exhaled by the animal and absorbed by the soda lime. Oxygen is absorbed by the animal from the inhaled air. Consequently air pressure inside the jar drops, and air from the room flows into the jar through the graduated pipette. This flow can be accurately measured by closing the end of the pipette with a film of soapy water. Air flowing into the tube from the room pushes the film, which serves as a pointer, ahead of it. Graduations indicate the internal volume of the tube at two points: one at five cubic centimeters and the other at zero c.c.

"The time required for the soap film to move from the zero graduation to the five-c.c. graduation is a function of the animal's metabolic rate. Measure this interval with a stop watch marked off in hundredths of a minute. Make three runs, add the three stop-watch readings, divide the sum by three and divide the resulting quotient into .3. The result represents the consumption of oxygen in liters per hour. Next square the recorded weight of the animal, find the cube root of the result and divide it by 1,000. This gives the approximate surface area of the animal in square meters. The ratio of the oxygen consumption per hour to the surface area is a measure of the animal's metabolic rate. This figure should be recorded in the appropriate column.

"The jar should be fitted with a floor of wire mesh to prevent the animals from coming into contact with the soda lime, as shown in the accompanying drawing [above]. Because soda lime reacts with the atmosphere, the spent chemical should be replaced with a fresh charge before tests are begun.

"The oxygen-consumption rate of each animal should be measured when the rats are put in their cages, and once every three days afterward during the 15-day period of the experiment. Ordinarily a correction factor for variations in atmospheric pressure and temperature is taken into consideration when computing the rate of oxygen consumption, but this may be omitted in the present experiment because the correction is small in comparison with experimental errors. If the initial rate of oxygen consumption of any rat varies more than 25 per cent from the average of those in all groups, the animal may be considered abnormal and should be replaced.

"A significant drop in oxygen consumption will follow the administration of PTU, although the drug requires about nine days completely to inhibit the action of the thyroid gland. The effect will be most apparent in Group III, which receives no replacing thyroxin. If Group II assimilates the foreign thyroxin, its reactions will match those of the control group (Group I) and the amount of oxygen consumed by the two groups will be similar. In contrast, the consumption rate of Group IV will in crease sharply, demonstrating the simulated effect of an overactive thyroid.

"The length and weight of each animal should be recorded at least as frequently as the rate of oxygen consumption. At the conclusion of the test run it is interesting to plot all data as graphs. Weight, growth and oxygen consumption for experimental and normal animals should be plotted as three separate graphs. The curves representing Group I and Group II should be similar. If not, then either the replacement dose was not correct in amount or the animal failed to assimilate the drug as anticipated. The hypothyroid group (those deprived of thyroxin) should show the lowest gain in weight and the hyperthyroid group the highest gain. The completed graphs illustrate the general influence of the thyroid gland on metabolism and growth under constant environmental conditions. The same inhibition-replacement technique can also be used to show how the thyroid helps the animal to cope with changes in its environment as well as how it modifies the action of selected vitamins, minerals and hormones other than thyroxin. It is interesting, for example, to investigate the role of the thyroid in helping an animal adapt to a cold environment.

"The four groups of rats are placed in an air-conditioned room (about 60 degrees F.) for three hours with water but without food. The oxygen-consumption test is then made. If the test proceeds normally, the results should show that the thyroids of the control animals respond to the temperature stimulus by stepping up the rate of oxygen consumption, suggesting an increased rate of thyroxin production. This implies that the thyroid plays an important role in helping warm-blooded animals to maintain constant internal temperature, a fact with important clinical implications. Patients with under-active thyroids feel unbearably cold at temperatures that are only mildly uncomfortable to most persons, a symptom that disappears when they are treated with the appropriate thyroid preparation.

"The experiment can be varied to study the effect on related hormones and assorted dietary deficiencies. One variation requires seven groups of experimental animals. One group is reserved as a- control. Three groups are treated as in the experiment described: one with PTU, the second with PTU plus a replacement dose of thyroid powder and the third with PTU plus a large overdose of thyroid powder. The remaining three groups receive precisely the same treatment plus daily injections of growth hormone. By comparing the slopes of the resulting rate-of-growth curves it will become apparent that growth hormone has little effect in the absence of a functioning thyroid gland. For the most interesting results the animals used in this experiment should be selected at the age when the normal rate of growth has become almost imperceptible. Similar experiments based on the inhibition-replacement technique can be designed for investigating vitamin-deficient and mineral-deficient diets. Materials for these, as well as the growth hormone experiment, can be purchased from the General Biological Supply House, mentioned earlier."

Frank Hughes, an amateur telescope-maker of Wausau, Wis., submits the design for a machine to grind and polish small telescope mirrors that approaches the ultimate in simplicity.

"Lately I have been turning my attention to grinding and polishing machines," he writes, "and have been looking for ways to lop off little pieces here and there without spoiling the basic mechanism. The result is a device s simple that it scarcely justifies the name 'machine.'

"Imagine a turntable on which a disk of thick glass, the 'tool,' is mounted. The surface of the mirror to be worked is placed on the tool with wet abrasive between the two. The mirror blank is loosely confined by three stationary buffer spaced at 120 degrees. If the tool, mirror and turntable are concentric an the buffers do not make contact wit the edge of the mirror (which has been edge-ground to a circle), the tool and mirror will simply rotate with the turntable. No work will be accomplished. If the turntable and tool are now offset by a fraction of the radius of the mirror, the mirror will be rotated by the tool against two of the buffers and will be abraded. Similarly, if the tool has been coated with pitch and rouge, the mirror will be polished. The polish will divide sharply, however, where the edge of the tool touches the mirror, and the resulting figure will suffer. If the tool is now offset on the turntable, the mirror will be pushed irregularly by the buffers with respect to the tool in a nonrepetitive path, the axial amplitude of which can be altered as desired. A turntable speed of about 30 revolutions can be used. The variables include the horizontal relationship of the turntable, the position and size of the triangle formed by the buffers and the eccentricity of the tool on the turntable. The turntable of my prototype is driven by a low-speed motor of an old ironing machine, and the buffers consist of three wooden slats fastened to the workbench. No cranks, no levers, no belting!"

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