246 DIGESTIVE SYSTEM. 



first place by the action of the gastric juice ; in the series of 

 processes which we have described (breaking down, liquefac- 

 tion, change of color), a series of decompositions occur, pro- 

 ducing tolerably well-defined intermediate peptones ; such as 

 the dyspeptone, the parapeptone, the metapeptone, and, 

 finally, the definite peptone. 



The dyspeptone is the residuum of digestion of the casein ; 

 it is quite insoluble, and cannot be assimilated. The charac- 

 teristic of the parapeptone is that it is precipitated by neu- 

 tralizing its acid solution; the metapeptone, on the contrary, 

 is precipitated by increasing the acidity of the product of 

 the stomach, and definitively by concentrated mineral acids. 

 These forms are only transitory, and as the digestion ap- 

 proaches its termination, they have all a tendency to change 

 into genuine peptones, with the exception of the dyspep- 

 tone which remains in its former state, and of the parapep- 

 tone, which shows a tendency to change into the same. 

 Some less important forms of transition have been observed 

 between the metapeptone and the definite peptone (peptone 

 A, peptone B), which are principally produced during the 

 digestion of the fibrine (Meissner, De Bary, Thiry). 



These transformations, especially the definite peptone, are 

 owing t6 the combined influence of the acid and the pepsin 

 of the gastric juice : these two elements of the digestive 

 fluid must act together. For instance, it would be useless to 

 operate on meat with hydrochloric acid, and then, after com- 

 plete washing, to place .it under the influence of a solution 

 of pepsin : in this case no peptones would be formed ; the 

 albumen only would be more or less entirely dissolved. On 

 the other hand, if pepsin and any acid ( T ^\>TT to To%tf ^ n 

 solution) be employed simultaneously, we can produce in 

 vitro artificial digestion, yielding nearly the same results as 

 natural digestion. 



The production of the real peptones must not be supposed, 

 however, to be one of those processes of transformation to 

 which the organism alone, or some growth (pepsin) bor- 

 rowed from the organism, can give rise. This transforma- 

 tion, like all the chemical transformations which we see 

 taking place in plants and in animals, shows no such mono- 

 poly of power as theorists of all ages have agreed in attrib- 

 uting to the agents of life. Peptones may be artificially 

 produced, but the process is long, and more curious than 

 practical. Meissner obtained perfect peptones from muscu- 

 lar flesh, with casein, legumin, etc. (albuminose by boiling. 



