FUNCTIONS OF PEPSIN. 55 



fore be cast away $ the maceration being then continued with a fresh por- 

 tion of cold water, and this being submitted to nitration, and subsequent- 

 ly evaporated at a low temperature to dry ness, yields the pepsin as a 

 gummy mass. From its solutions pepsin may be precipitated by corro- 

 sive sublimate or acetate of lead, and it may be separated from those 

 combinations by sulphureted hydrogen. Wasmann availed himself of 

 this fact to obtain it in a pure state. 



Composition of Pepsin. (From Schmidt.*) 



Carbon 530.00 



Hydrogen 67.00 



Nitrogen 178.00 



Oxygen 225.00 



1000.00 



From this it would appear that it contains less carbon and more nitro- 

 gen than the members of the protein group. 



A weak acid therefore possesses at a high temperature the power of 



bringing into a state of solution the various nitrogenized food _ 



-II -. o -1 <> i - Pepsm re- 



matters, and at lower degrees fails of that property ; but in places a high 



the presence of pepsin the solvent powers are assumed un- tem P eratur e. 

 der the latter circumstances, and therefore it is said of this substance 

 that it replaces a high temperature. By its aid, hydrochloric or lactic 

 acids present in the stomach reduce the food to a uniform pulpy mass 

 the chyme. Of all acids, these, however, alone arc capable of forming 

 digestive fluids. 



Formerly it was supposed that the act of digestion was simply me- 

 chanical, the food being ground down to chyme by the mo- R ex 

 tions of the stomach. Reaumur's experiments showed the perimcntswith 

 error of this supposition. He took small hollow silver balls, Sllver balls * 

 perforated with holes, and, having filled them with meat, caused them to 

 be swallowed by a dog. When they had remained in the animal's stom- 

 ach a suitable length of time, they were withdrawn by a thread which 

 had been previously attached to them. Now if the stomach acted by a 

 triturating or grinding power, the material within the ball would be en- 

 tirely protected, but if by a solvent power exerted by the gastric juice, 

 the digestion should at most be only delayed. Accordingly, it was found 

 that this was what actually took place, digestion being fully, though more 

 slowly accomplished, the action commencing on the outside of the mate- 

 rial, and gradually reaching its centre. If the balls were kept in the 

 stomach long enough, they came out quite empty at last. 



The idea that there is something more than a simple solution of the 

 food effected in the stomach, that some mysterious change is Chief object of 

 impressed upon it by the vitality of that organ, may there- tSrthe^oiu" 

 fore be abandoned. It does not appear that there is any es- tionofthefood. 



