LAWS GOVERNING METABOLISM. 443 



AN EXCLUSIVE DIET OF FATS OR CARBOHYDRATES. 



If fat alone is supplied, the body is unable to maintain itself. In consequence 

 of the deficiency of nitrogen, the animal must necessarily perish. The symptoms 

 occurring with this form of diet are as follows : The animal in question secretes less 

 urea than in a state of hunger. Therefore, the consumption of fat must restrict 

 that of the flesh of the animal itself. This is due to the fact that the fat, being 

 a readily combustible substance, is more readily oxidized in the body than the 

 less readily combustible nitrogenous albuminates. If the amount of fat taken 

 is exceedingly large, not all of the carbon of the fat can be recovered in the excreta, 

 or as carbon dioxid in the expired air. Accordingly the body must accumu- 

 late fat, while naturally it destroys proteids in corresponding amount. The 

 animal thus becomes fatter and at the same time poorer in flesh. 



The result of administration of carbohydrates alone, which must first be con- 

 verted into sugar by the digestive processes, exhibits marked similarity to that 

 obtained with a pure fat-diet. It should, however, be noted that the sugar in 

 the body more readily undergoes destruction than the fat, and, further, that with 

 reference to the nutritive value, 256 parts of glucose are the equivalent of 100 

 parts of fat. Accordingly, a carbohydrate-diet restricts the decomposition of 

 proteids even more readily than a pure fat-diet. 



Just as it is necessary outside of the body for the fermentation of disaccharids 

 and polysaccharids that these be first decomposed into monosaccharids, so also 

 the combustion of sugar in the body can occur only on condition that a trans- 

 formation into monosaccharids has previously taken place. 



LAWS GOVERNING METABOLISM ON A MIXED DIET OF MEAT 

 AND FAT OR CARBOHYDRATES. 



If a dog in a state of metabolic equilibrium be given an amount of fat and 

 starch exceeding its requirements, elimination through metabolism is not in- 

 creased, but the excess of these non-nitrogenous foods administered is deposited 

 in the body of the animal as fat. 



If a dog fed with the leanest possible meat, and in a state of metabolic equilib- 

 rium, be given an additional amount of meat exceeding its requirements, the 

 elimination through metabolism increases almost proportionately to the addi- 

 tional amount administered beyond the requirements. Only a small portion of 

 the addition is conserved and increases the body-weight as a deposition of flesh. 

 This augmentation of metabolism not only causes an increase in the nitrog- 

 enous excretion in general proportional to the supply of proteid, but also the 

 carbon contained in the supply of proteid is again excreted, for of the proteid 

 fed no portion is deposited in the body as fat or carbohydrate. From both of 

 these statements it follows that neither fat nor carbohydrate is capable of in- 

 creasing metabolism beyond the requirements, although proteid is. 



The seat of active proteid metabolism after a diet rich in proteids is, 

 according to Pfliiger, not in the increased flow of fluid, but within the proteid- 

 containing cells which have undergone a marked alteration (saturation) as a 

 result of the entrance of the proteid into them. This view is confirmed by the 

 experiments of Schondorff, who found that if the blood of a fasting animal be 

 forced through the tissues of a generously nourished animal the urea in the blood 

 of the latter increases, while, on the contrary, if the blood of a well-nourished 

 animal be forced through the tissues of a fasting animal the urea in the blood 

 of the latter diminishes. As, on providing an adequate amount of proteid, mus- 

 cular activity takes place only at the expense of proteid, and as in the decomposi- 

 tion of this proteid neither fat nor carbohydrate results, fat or carbohydrate 

 cannot be the source of muscular activity (Pflugcr). Other investigators are 

 of the opinion, however, that with adequate nitrogenous nourishment energy as 

 well as heat can be generated from fat and carbohydrate. 



Nourishment with Carbohydrates and Meat. The organism is capable of gen- 

 erating fat from carbohydrates. A deposition of fat in the body thus brought 

 about takes place only if in addition to the proteid of the meat a nutritive excess 

 of carbohydrates is present. Such an excess of starch may be present even when 

 the supply of starch itself is small, while the excess may even be wanting when 

 the supply of starch is large. The result depends upon the character of the food 

 that is supplied in addition to the starch. The larger the amount of proteid, in 



