36 THE SECRETIONS: 



mation of chyle, which as we know is always tolerably con- 

 stant in its composition, although evolved from the most di- 

 verse species of nutriment. 



Previously to commencing such researches, it would be re- 

 quisite to study and examine the pepsin obtained from different 

 classes of animals ; for it is very possible, as Berzelius suggests, 

 that it may be a mixture of various substances, differing in dif- 

 ferent classes of animals. On this account, various simple natural 

 substances, after the addition of a due quantity of acid (which must 

 be determined experimentally,) should be artificially digested 

 with the different sorts of pepsin, and the products, both soluble 

 and insoluble, carefully analysed. Such terms as osmazome, 

 salivary matter, &c. must be rejected. The researches of 

 Berzelius and myself have opened the way for an exact and 

 separate determination of the extractive matters and ptyalin. 

 "We should then be enabled to see what real connexion there is 

 between the substances resembling extract of flesh which are 

 produced in artificial digestion, and those that are actually 

 obtained from flesh itself. 



Our knowledge of the changes that the different elements of 

 food undergo in the process of digestion is at present very 

 limited; it is confined to the following leading points. 



1 . Albumen is dissolved and chemically changed. This ob- 

 servation was made by Eberle, and has been confirmed by 

 Miiller, Schwann 1 , and others. The digested albumen no longer 

 coagulates at the boiling point ; it is stated to have been changed 

 into osmazome and salivary matter, (a vague statement requiring 

 further proof,) and according to Schwann, into a third albumi- 

 nous principle, which is thrown down by carbonate of soda, and 

 in that condition is insoluble in water and spirit, soluble in 

 muriatic and acetic acids, and not precipitable by acetate of lead 

 or alcohol, but copiously by nitric acid and bichloride of mer- 

 cury, and partially by ferrocyanide of potassium and tannic 

 acid. 



2. Coagulated casein is partially converted by artificial di- 

 gestion into albumen ; soluble casein becomes coagulated when 

 submitted to the action of a solution of sugar of milk and 

 pepsin, but not when acted on by the pepsin alone. 



3. Fibrin is rapidly dissolved, and, from the experiments of 



1 Muller's Archiv, 1836, p. 68. 



