434 HANDBOOK OF PHYSIOLOGY. 



trogenous extractives and uric acid will be seen by a reference to their 

 iunnulig: 



Hypoxanthin or Carnin C B H 4 N 4 O. 



Xanthin C B H 4 N 4 O2. 



Uric Acid C 6 H 4 N 4 O 3 . 



Formation of Hippuric Acid. The source of hippuric acid is not sat- 

 isfactorily determined; in part it is probably derived from some constit- 

 uents of vegetable diet, though man has no hippuric acid in his food, 

 nor, commonly, any benzoic acid that might be converted into it; in 

 part from the natural disintegration of tissues, independent of vegetable 

 food, for Weismann constantly found an appreciable quantity, even when 

 living on an exclusively animal diet. Hippuric acid arises from the 

 union of benzoic acid with glycin (C 2 H 5 N0 2 + C 7 H 6 2 = C 9 H 9 N0 3 + 

 H 2 0), which union probably takes place in the kidneys themselves. It is 

 possible that the aromatic radicle in this reaction is obtained from the 

 splitting up of tyrosin, which appears so frequently as a result of the 

 decomposition of proteid, the ammonia radicle with which it is associ- 

 ated going to form urea. 



The source of the extractives of the urine is probably in .chief part 

 metabolism of the nitrogenous tissues, but we are unable to say whether 

 these nitrogenous bodies are merely accidental, having resisted further 

 decomposition into urea, or whether they are the representatives of the 

 decomposition of special tissues, or of special forms of metabolism of 

 the tissues. There is, however, one exception, and that is in the case 

 of kreatinin ; this represents not only the kreatinin which enters the 

 body in ordinary flesh food, but nitrogenous waste as well. 



Effects of Fats and Carbohydrates as Food. Experiments illustrating 

 the ill-effects produced by feeding animals upon one or two alimentary 

 substances only have been often performed. 



Dogs were fed exclusively on sugar and distilled water. During the 

 first seven or eight days they were brisk and active, and took their food 

 and drink as usual; but in the course of the second week they began to 

 get thin, although their appetite continued good, and they took daily 

 between six and eight ounces of sugar. The emaciation increased during 

 the third week, and they became feeble, and lost their activity and ap- 

 petite. At the same time an ulcer formed on each cornea, followed by 

 an escape of the humors of the eye : this took place in repeated experi- 

 ments. The animals still continued to eat three or four ounces of sugar 

 daily ; but became at length so feeble as to be incapable of motion, and 

 died on a day varying from the thirty-first to the thirty-fourth. On dis- 

 section their bodies presented all the appearances produced by death from 

 starvation ; indeed, dogs will live almost the same length of time without 

 any food at all. 



When dogs were fed exclusively on gum, results almost similar to the 



