Convincing as these experiments may seem to the average lay mind they did not meet the old argument, drawn from certain experiments upon dogs, that high-proteid animals cannot live and thrive for any great length of time on the low proteid diet, and that, therefore, while man, as a moderate proteid-eater, can endure for a while even large reductions in proteid food he will eventually manifest some of the disastrous results obtained experimentally with dogs.

9 Chittenden: "Physiological Economy in Nutrition," p. 438,

Therefore Professor Chittenden's next step was to demonstrate that these old experiments proved nothing at all except that any animal will not thrive if kept in close confinement under unhygienic conditions and fed on a monotonous diet. Accordingly the twenty dogs used in his experiment were kept under scrupulously hygienic conditions and fed on a diet sufficiently varied to be tempting to the appetite, although containing only about one-half to one-third the amount of proteid food to which the dogs had been accustomed.

Professor Chittenden's account of his observations on one of his subjects is as follows:

"The animal employed in this experiment weighe4 on July 27, 1905, 17.2 kilograms

(37.9 pounds); it was apparently full grown, but was thin and had the appearance of being underfed. At first, it was given daily 172 grams (52/3 oz.) of meat, 124 grams

(41/6 oz.) of cracker dust, and 72 grams (21/3 oz.) of lard, the day's ration containing

8.66 grams of nitrogen and having a fuel value of 1389 calories.10 These figures are equivalent to 80 calories, and 0.50 gram of nitrogen, per kilogram (2.204 pounds) of body-weight. The animal took kindly to the diet, but on August 3 it refused to eat and seemed to have a little fever. The next day it was better, but for the three following days its appetite was poor, and only a portion of the daily food was eaten. Body-weight began to fall off, and was soon at 15.5 kilograms (34.16 pounds). On the 7th of August, a dose of vermifuge was given, after which the appetite returned and the animal appeared in good spirits. From this time forward it seemed in perfect health, with good appetite, and showed the usual vivacity and playfulness of dog-kind. The diet as specified was continued unchanged until August 25, a balance experiment covering a period of ten days, from the 15th to the 24th of August inclusive, being carried out, in which the nitrogen of the intake was compared with the output for each day. ... During this first period the animal was laying on or gaining an average of 2 grams of nitrogen per day.

10"'A calorie may be defined as the amount of heat required to raise one gram of water 1 degree C. This unit is usually spoken of as the small calorie to distinguish it from the large calorie, which represents the amount of heat required to raise one kilogram of water 1 degree C Hence, the large calorie is equal to one thousand small calories. When burned in a calorimeter, one gram of carbohydrate yields on an average 4100 gram-degree units of heat, or small calories; one gram of fat yields 9300 small calories. Both of these non-nitrogenous foods burn or oxidize to the same products - viz., carbon dioxide and water - when utilized in the body as when burned in the calorimeter; hence the figures given represent the physiological heat of combustion, per gram, of the two classes of food stuffs. Obviously, the fuel values of different foods belonging to the same group or class will show slight variations, but the above figures represent average values." - Chittenden: " Nutrition of Man," p. 14.

"On August 25, a radical change was made in the diet, by reducing the amount of meat to 70 grams (2 1/3 oz.) daily, thereby lowering the intake of nitrogen to 4.76 grams or 0.27 gram per kilo of body-weight; the cracker dust and lard being kept at essentially the same levels as before. This diet was continued through the next balance period, the dog in the meantime gaining in body-weight, and showing for the second balance period an average gain by the body of half a gram of nitrogen per day. The food was then altered by substituting bread for cracker dust, but so adjusted that the nitrogen and fuel values of the day's food remained practically unchanged. There was still, however, a gain in body-weight and a slight gain in body nitrogen. At the close of the third balance period, the diet was again altered, one-half of the meat being replaced by milk, while cracker dust was substituted for the bread. The morning meal consisted of 170 grams (5 2/3 oz.) of milk, 86 grams (3 oz.) cracker dust, and 18 grams (§ oz.) of lard, while the afternoon meal was composed of 35 grams (1 1/6 oz.) of meat, 63 grams (2 oz.) of cracker, and 35 grams (l 1/6 oz.) lard. The day's ration, however, still contained 4.76 grams of nitrogen and had a fuel value of 1249 calories.

This diet was maintained until November 20, when the animal was again placed on a daily ration of meat 69 grams (2 1/3 oz.), bread 166 grams (5½ oz.), and lard 80 grams (22/3 oz.) with a total fuel value of 1228 calories and 4.77 grams of nitrogen.

This was continued until December 2, the dog still showing a plus nitrogen balance, but with a little loss in body-weight. On December 2, the diet was again changed by-substituting milk for a portion of the meat, but the nitrogen and fuel values were maintained at the same level as before. After a week, December 9, the food was modified as follows: the morning meal contained 170 grams (52/3 oz.) of milk, 110 grams (32/3 oz.) of rice, and 11 grams (1/3 oz.) of lard, while the afternoon meal was composed of 35 grams (l1/6 oz.) of meat, 81 grams (22/3 oz.) of rice, and 30 grams (1 oz.) of lard. The total nitrogen content of the day's ration was 4.07 grams, while the fuel value was 1255 calories. At this time, the animal weighed 17.1 kilograms (37.68 pounds), consequently the intake of nitrogen had been reduced to 0.23 gram per kilo of body-weight, while the fuel value stood at 73 calories per kilogram. This diet was continued until February 9, the balance period, between January 2 and 11, showing that the animal was in nitrogen equilibrium, in spite of the material reduction in the intake of proteid, and that body-weight was increasing. The next balance period, January 30 to February 8, showed still further gain in weight with continuance of nitrogen equilibrium.