LECT. V. AZOTISED SUBSTANCES. 101 



number of the animal tissues and fluids, is analogous to the 

 organic neutral substances now referred to ; and since, more- 

 over, in becoming part of the animal organism they undergo' 

 no change of chemical composition, but merely acquire 

 during nutrition a new form, it is fair to assume that, in the 

 act of digestion, the azotised neutral alimentary substances 

 merely dissolve in order to pass, without any other altera. 

 tion, into the blood. 



The isomerism of these substances is equally demonstrated 

 by the beautiful discovery of Denis, that fibrine is converted 

 into albumen by dissolving it in a saturated solution of nitre. 

 This fact is the more curious, because it appears to hold 

 good for the fibrine of venous blood only ; the fibrine of 

 arterial blood, neither dissolving in a solution of this salt, 

 nor becoming converted into albumen. Scherer has tried 

 the effect of exposing the fibrine of venous blood to an at- 

 mosphere of oxygen, and found that the oxygen was con- 

 verted into carbonic acid, and the fibrine thereby lost its 

 property of being convertible into albumen by a solution of 

 nitre. 



Some physiological experiments have long siftce proved, 

 that the digestion of similar alimentary substances is a purely 

 physical act, which takes place independently of the living 

 organism. No one is ignorant of the celebrated experi- 

 ments of our countryman Spallanzani : meat, gluten, and 

 coagulated albumen, introduced into the stomach in perfo,. 

 rated metallic tubes, were dissolved and digested, as though 

 they had been free in the stomach. This solution is effected^ 

 as we shall presently find, by means of one of those actions 

 of which we spoke in our first lecture, and which have been 

 called catalytic or actions of contact. 



The recent experiments of Melsens, and especially those 

 of Bernard and Barreswil, have shown, that the gastric juice 



