902 NUTRITION AND HEAT REGULATION. 



ally undergoes oxidation in the body with the production of carbon 

 dioxid, water, and urea. The energy liberated by this metabolism 

 is utilized no doubt in the body, and the gelatin constitutes an 

 "energy-food" similar in a general way to the carbohydrates and 

 fats, although its various amino-acids must give it to some extent 

 a special significance. The important point in this connection is 

 that gelatin alone or with carbohydrates or fats does not suffice to 

 maintain nitrogen equilibrium. It does not supply fully the 

 nitrogenous material needed for the repair of tissue. This defi- 

 ciency is explained by the fact that in the composition of the gelatin 

 certain important amino-acids are lacking, tryptophan (indolami- 

 nopropionic acid), tyrosin (oxyphenylaminopropionic acid), and 

 cystein (thioaminopropionic acid) . It is stated that if a dog is fed 

 upon a diet in which the nitrogenous material is represented only 

 by the split products of a gelatin-hydrolysis he will show a minus 

 nitrogen balance, but if the above-named missing amino-acids are 

 added, particularly the tryptophan, he will then maintain his 

 nitrogen equilibrium. 



The history of gelatin as a food is very interesting and, indeed, instructive, 

 since it serves or should serve as a warning against a premature application 

 of the results of scientific investigation. A condensed account of the subject 

 is given by Voit in Hermann's Handbuch der Physiologic, vol. vi., p. 396. 

 It would seem that on account of the high nitrogen content of the gelatin, and 

 the fact that it is soluble, there was a tendency to attribute to it an unusual 

 nutritive value. The fact, too, that the gelatin could be obtained from bones 

 which otherwise were burned or thrown away was important in suggesting 

 a means for the economical feeding of the poor. The matter was inquired 

 into by a committee during the French Revolution and subsequently by a 

 commission of the French Academy, who made favorable reports. The success 

 of d'Arcet, in making gelatin economically by a new process, led the Philan- 

 thropic Society of Paris to request the Academy of Medicine to investigate 

 whether gelatin is really a nutritious and healthy food. The Academy 

 appointed a commission for the purpose and the report of this commission 

 published in the Annales de Chimie, vol. 92, 1814, was most enthusiastic. 

 They recommended gelatin as a most nutritious and healthful food, when its 

 natural insipidity was corrected by the addition of salts and savory herbs. 

 On the basis of this report the article was largely used in the nourishment of 

 hospital patients, but in course of time complaints became so emphatic that 

 doubt was again raised as to its real value. In fact, a reaction set in. The 

 second gelatin commission of the French Academy, 1841, a commission of 

 the Netherland's Institute, 1844, and a report from the Academy of Medicine, 

 Paris, 1850, all condemned gelatin as useless from the standpoint of nourish- 

 ment, and as injurious rather than beneficial. Thus, as so often happens, 

 public opinion oscillated from one extreme to the other. The true value 

 of the gelatin, as we understand it to-day, was established by Voit's experi- 

 ments, but it is evident that something remains to be explained. It is not 

 clear why it cannot be borne better in a diet when used in quantity. 



Most suggestive results on this question of the nutritive values 

 of the different proteins have been obtained in a series of experi- 

 ments reported by Osborne and Mendel.* These observers made 



* Osborne and Mendel, "Carnegie Institution of Washington, Publication 

 156," parts I and II, 1911; also "Journal of Biological Chemistry," 12, 473, 

 1912; 13, 233, 1912, and 15, 311, 1913. 



