NATURE AND DESTINATION OF FOOD. 377 



been already sufficiently considered (CHAP. n). The proportions of carbon, 

 hydrogen, oxygen, and nitrogen, of which all these substances are composed, 

 appear to be identical; and they are all capable of being reduced by the digestive 

 process to the condition of albumen. Hence it is a matter of little consequence, 

 except as regards the proportions of inorganic matters with which they may be 

 respectively united, whether we draw our histogenetic materials from the flesh 

 of animals, from the white of egg (albumen), from the curd of milk (casein), 

 from the grain of wheat (gluten), or from the seed of the pea (legumin). 

 Neither of these substances, however, can long sustain life when it is used by 

 itself; for it has been experimentally ascertained that, by being made to feed 

 constantly on the same substance boiled white of egg, for instance, or meat 

 deprived of the principle (osmazome) that gives it flavor an animal may be 

 effectually starved; its disgust at such food being such that, even if this be 

 swallowed, it is not digested. 1 The organized fabric of Animals contains, as we 

 have seen, a large quantity of Gelatin. It seems certain that this substance 

 may be produced out of fibrin and albumen ; since in animals that are supported 

 on these alone, the nutrition of the gelatinous tissues does not seem to be im- 

 paired. But it has been commonly supposed that gelatin taken in as food may 

 serve for the growth and maintenance of these tissues ; even though it may be 

 incapable of conversion to the albuminous type. It is very doubtful, however, 

 whether Gelatin can render even this service. For all our knowledge of the 

 history of the development of the Gelatinous tissues would lead us to regard 

 them as secondary products, which take their origin in a fibrinous blastema, and 

 can only be generated by the metamorphosis of protein compounds ( 28, 29, 

 222, 223). If these views be correct, it follows that the alimentary value of 

 gelatin must be limited to its calorific power ; its hydrocarbon being separated 

 from its highly azotized portion, and the former being oxidized and eliminated 

 through the lungs, whilst the latter will pass off by the kidneys. And this 

 view is confirmed by the observations of Frerichs on the result of the ingestion 

 of large quantities of pure gelatin; this being a marked increase in the propor- 

 tion of urea in the urine, with an elevation of its specific gravity from 1018 to 

 1030 or even 1034. Neither Leucine nor Glycine could be detected in the 

 fluid; so that Gelatin seems to be subjected to the same metamorphosis that 

 the protein compounds undergo when they are taken in excess. 2 That Gelatin 

 cannot take the place of the albuminous compounds, has been fully demon- 

 strated by the inquiries of the Commissions which have been appointed to in- 

 vestigate the subject in Paris and Amsterdam. 3 In so far, therefore, as the 

 only azotized principles contained in soups, broths, &c., are of the gelatinous 

 character, we must account these preparations as destitute of the power of 

 nourishing the body ; and the peculiar nutritive value which experience shows 

 that such preparations possess in certain states of the system, must be attributed 

 to the albuminous matters which they hold in solution, and to the readiness 



1 It is very interesting to remark (with Dr. Prout) that, in the only instance in which 

 Nature has provided a single article of food for the support of the animal body, she has 

 mingled articles from the three first of the preceding groups. This is the case in Milk, 

 which contains a considerable quantity of an albuminous substance, casein, which forms 

 its curd ; a good deal of oily matter, the butter ; and no inconsiderable amount of sugar, 

 which is dissolved in the whey. The proportions of these vary in different Mammalia ; 

 and they depend in part upon the nature of the food supplied to the Animal that forms 

 the milk ; but the substances are thus combined in every instance. 



2 See Frerichs's article Verdauung in "Wagner's Handworterbuch." The Author is 

 indebted to Dr. Gull for directing his attention to this view of the incapacity of Gelatin 

 for any histogenetic purpose. 



3 See the Report of the French "Gelatin Commission," in the " Compt. Rend." Aout, 

 1841; and that of the Amsterdam Commission in "Het. Instituut," No. 2, 1843, and 

 "Gazette Medicale," Mars 16, 1844. 



