LECT. VII. COMBUSTION DURING CIRCULATION. 141 



An important observation recently made by Dessians de- 

 serves to be noticed here. By boiling hippuric acid with a 

 solution of hydrochloric acid, benzoic acid was precipi- 

 tated and hydrochloric acid obtained in solution, combined 

 with a saccharine azotised matter, which was found to be 

 Braconnot's gelatine-sugar. We know that this substance 

 (gelatine-sugar) is obtained by treating neutral azotised 

 matters (proteine and gelatine) with acids. We further 

 know that hippuric acid replaces, in the herbivora, the se- 

 cretion of urea in the carnivora. We may infer from this, 

 that gelatine-sugar is one of the first products of the trans- 

 formation of neutral azotised matters, which are the mate- 

 rials of the tissues. We may thus comprehend how, by 

 adding benzoic acid, which combines with them, hippuric 

 acid may be obtained. 



Combustion during Circulation. All these facts prove 

 beyond doubt that the principal chemical action observed 

 in the circulation of the blood, and in nutrition, is a com- 

 bustion, that is, a combination of oxygen with the carbon 

 and hydrogen of the organic tissues. But, I repeat, up to 

 the present time, great obscurity prevails in our knowledge 

 of the series of these phenomena. What difference exists 

 between the chemical composition of all the elements of the 

 arterial blood, and that of all the elements of the venous 

 blood ?* What is the nature of this difference in the blood 



* According to Dr. G. O. Rees (Proceedings of the Royal Society, for 

 June 3d, 1847,) venous blood contains a phosphoric fat, and arterial blood, 

 a tribasic phosphate of soda. " The venous corpuscles are known to con- 

 tain fat in combination with phosphorus. This compound ingredient of 

 the corpuscles, on coming into contact with atmospheric oxygen during 

 the respiratory act, is consumed, and combining with that oxygen, forms 

 the carbonic acid and water which are expired ; and also phosphoric acid, 

 which, uniting with the alkali of the liquor sanguinis, forms a tribasic 

 phosphate of soda. This salt, like many others, acts upon hcematosine in 

 such a manner as to produce the well-known bright arterial tint." J. P. 



