Experimental Methods

During the past four years the author, in conjunction with Dr. Miller and Mr. Karshan, and under the supervision of Prof. Gies, has carried out a series of nutritional experiments with rats that were intended to illustrate some of the fundamental facts of the science taught to medical and graduate students (as a part of the course in physiological chemistry required of students of medicine at Columbia). These experiments were in the form of demonstrations and were intended as supplements to the practical work carried out by students in the laboratory. From the mass of data that has been accumulated, a few experiments will be selected to illustrate several portions of the text.

Preliminary Details

In most cases it is desirable to start the experiment with young rats - rats weighing anywhere from 50 to 70 grams (approximately 30 grams are the equivalent of one ounce). For any one experiment two sets of animals are selected, one A to act as the "control," and the other B as the "experimental" group. These sets are so selected as to make both the control and experimental groups represent similar stocks. The animals should be either all males or all females. To illustrate: In one particular experiment the source of supply came from three litters. From each litter four rats were selected, two of them being put in group A (control) and two in group B (experimental ). A certain amount of balancing of weights when the rats are grouped is necessary so that, at the start of the experiment, the control animals weigh approximately the same as the experimental animals.

The cages provided for the animals are those devised by Prof. Gies. They consist of rectangular iron boxes, with wire screens covering the top and the front. The top acts as a door. This can be easily removed, coarse sawdust spread on the floor, and two containers, such as porcelain mortars or small glass jars, are put in. One of these is usually filled with water and the other with the solid food. If desired, a partition attachment can be used, so that one cage may house both sets of rats.

It is of the utmost importance to pay much attention to the hygienic conditions. The cages must be thoroughly cleaned every day. The room in which the cages are placed should be a desirable one from the point of view of light, temperature and air.

In the beginning, say for the first few days, it is desirable to weigh the rats daily. As the trend of the experiment becomes apparent, such weighings may become less frequent - perhaps once or twice a week.

The weighings are carried out by putting the animals in a fair-sized tin can, with perforated cover, the weight of which is known, and weighing can plus rats. Usually from four to six rats are weighed at one time, these representing sets belonging either to group A or B. The average weight is then determined by dividing the total weight by the number of rats in the can.

While the progress of an experiment is very largely determined by the change in weight of the rats, a careful daily inspection of the animals with the view to locating possible physical defects, is highly desirable.

As has already been pointed out in the text, rats are by no means the only animals that can be employed for experimental purposes; indeed, in some cases, as when testing for the anti-scorbutic vitamine, they are of no value at all, since they are not susceptible to scurvy. Here guinea-pigs are usually made use of. For quick responses in the case of vitamine B - the anti-beriberi vitamine - pigeons are used. For a careful study of the symptoms of rickets, pups serve excellently.

It should also be pointed out that very rarely do any two laboratories adopt exactly the same methods of procedure. There is, in fact, much variation on this point; far more so than is desirable, if uniform results are to be obtained.

The Effect of an Exclusive Meat Diet. The "controls" A and "experimental" B * consisted of six rats each. A were fed on the "regular diet,"

- one known from experience to serve as an excellent diet for rats. This consisted of turnips and cheese the first day; bread and rye the second; corn and meat the third; bread and milk the fourth; meat and cabbage the fifth; bread and milk the sixth; then a cyclic repetition from the first day.

* In all of the experiments described here A represent the "controls," and B the "experimental" animals.

For the first few days the experimental animals were also fed on the regular diet. This is always done to make sure that such animals have the capacity to grow, and also to show where the treated ones should, theoretically speaking, be at a given time.

In this experiment, as well as in those that follow it, only a few significant figures will be given. The weights represent the average weight of each group.

Weights on the first day of the experiment:

A 73 1 B 75

For four days both sets received the regular diet. Weights at the end of the fourth day:

A 93 B 96

From now on A received the regular diet and B meat (in the form of raw "hash") only.2 On the 75 day the weights were:

A 230 B 207

1 The numbers refer to grams.

2 Unless expressly stated to the contrary, it is assumed that plenty of water is provided. In the experiments described here the amount of food provided was such that at no time were the mortars empty. This is of course a very important point. In some experiments it becomes necessary to keep a record of the exact intake of food.

The meat diet received by B was now replaced by the regular diet. On the 92 day the weights were:

A 240 B 235

We may conclude, then, that the meat diet is not "quite as good" as the regular one, though the differences are not very striking for the age and period involved.3