12 CHEMICAL PHYSIOLOGY. 



and peptones alone. There are also undigested pieces 

 of flesh, albumen, caseine, constantly present. It is 

 at present impossible to say what these albuminous 

 matters are. Some physiologists say there is only one 

 substance, others that there are five and more, the 

 statements as well as the experiments upon which 

 they are based being quite irreconcileable with each 

 other. None of these researches have as yet been 

 carried out by means of the quantitative chemical 

 method, excepting the comparison of the compo- 

 sition of the peptones with the original matters. 

 It was found to be almost unchanged. The pep- 

 tone solutions are not coagulated by boiling, but are 

 precipitated by absolute alcohol. They give Millon's 

 reaction with nitrate and nitrite of mercury. They 

 diffuse easily through parchment paper (dialyse) into 

 water, exhibiting a property towards membranes of 

 the utmost importance for absorption, which albumen 

 possesses only in the very slightest degree. Optically 

 they are characterised by turning the plane of polarisa- 

 tion towards the left. 



The coagulation of milk in the stomach, or by 

 rennet out of it, is supposed by some to be due not 

 to pepsine, but to another ferment which transforms 

 sugar of milk or lactose into lactic acid, and pre- 

 cipitates the soda-albumen or caseine. This matter 

 is problematical. 



The quantity of gastric juice secreted daily in the 

 human stomach has been estimated at 10 per cent, 

 of the body- weight, or 16 Ibs.; other direct observations, 

 however, lead to 30 Ibs. 



