468 HISTORICAL. 



in association with xanthin occurs in many organs and in urine. Kossel suc- 

 ceeded in preparing hypoxanthin from nuclein b)^ prolonged boiling. It can be 

 obtained from fibrin by putrefaction and the action of gastric and pancreatic 

 juice. Xanthin can be produced from hypoxanthin by oxidation and is con- 

 vertible into caffein. Xanthin and guanin have been produced synthetically by 

 Gautier. Paraxanthin and heteroxanthin occur in the urine; carnin, which re- 

 sembles them, in meat. An intermediate stage between nuclein. and hypoxanthin 

 is represented by the adenin (C 3 H 5 N 5 ) of Kossel, which has _ been found in the 

 spleen, the pancreas, the thymus, the seminal fluid, and also in tea and in yeast. 

 It appears to occur as an amorphous powder, or in six-sided columns disintegrating 

 in the air, and as a decomposition-product of nuclein in all animal and vegeta- 

 ble cell-tissues. 



AROMATIC BODIES. 



i. M anatomic phenols: (a) The phenol (hydroxl or benzol) in the intestine; 

 phenylsulphuric acid in the urine. (b) Kresol in the form of orthokresol, meta- 

 kresol and parakresol combines with sulphuric acid in the urine. (2) Diatomic 

 phenols: (a) Pyrocatechin combined with sulphuric acid in the urine. (3)^ Aro- 

 matic oxy acids: (a) Hydroparacumanc acid; (6) Paroxyphenylacetic acid in the 

 urine. (4) Substituted carbohydrates: (a) Indol (also prepared artificially) and 

 (b) skatol both occur in the intestine and combined with sulphuric acid in the 

 urine. Stoehr has prepared skatol artificially by distillation of strychnin with 

 calcium. 



HISTORICAL. 



According to Aristotle the body requires food for three purposes, namely 

 for growth, for the generation of heat and to compensate for loss from the body. 

 The generation of heat was thought to take place in the heart by a process of 

 concoction, the heat being carried with the blood to all parts of the body, while 

 the act of respiration was considered as a means for dissipating the excess of heat 

 generated in the process of combustion. In a somewhat modified form also Galen 

 held this view. According to him the metabolism is comparable to the conception 

 of a lamp, the blood representing, to a certain degree, the oil, the heart the wick, 

 and, finally, the lungs the draft. According to the view of the iatrochemical 

 school, metabolism takes place in the body in the form of fermentative processes 

 in which the substances introduced are decomposed in conjunction with the 

 bodily juices. There thus result refined, useful juices, and fermentative waste 

 products intended for excretion. Since the middle of the seventeenth century 

 knowledge of the metabolic processes has progressed hand in hand with the devel- 

 opment of chemistry. A. v. Haller ascribed the heat to chemical processes. He 

 believed that the nourishment must make good to the body the constant loss 

 of excrementitious matter. Anabolism takes place through a lymphatic fluid, 

 which is poured out for the reconstruction of the used-up animal fibers between 

 the latter. Mayow believed in 1679 that metabolism was essentially a process 

 of combustion, the blood becoming bright red in the lungs. After the discovery 

 of oxygen Lavoisier formulated the theory of combustion in the lungs, in which 

 he believed carbon dioxid and water were formed. He compared the relatively 

 slow course of physiological combustion with the heating of dung that takes 

 place at a lower temperature. Mitscherlich compared the metabolic processes in 

 the living body directly with putrefactive phenomena. Magendie first pointed 

 out the difference between nitrogenous and non-nitrogenous foods and showed 

 that the latter alone are not capable of sustaining life. Also gelatin alone is 

 insufficient for this purpose. His results were less precise with respect to the 

 nutritive value of albuminates, which he nevertheless gave foremost rank, and 

 among which he was willing to recognize only meat as adequate as nutritive 

 material. 



The greatest advance in the principles of nutrition is due to J. Liebig, who 

 laid the foundation of the present knowledge of metabolism. According to his 

 view food-stuffs subserve two purposes, namely as plastic, for the growth of the 

 body, and, as respiratory, for the generation of heat. The former includes espe- 

 cially the albuminates, the latter especially the non-nitrogenous carbohydrates 

 and fats. 



Among recent investigators the Munich school deserves especial mention as 

 advancing knowledge: v. Bischoff, v. Pettenkofer, v. Voit and others. Most 

 recently Pfliiger has made important contributions. 



