446 EESPIRATION. 



in a crystalline form. Its quantity is not very great. The 

 lungs of a female who suffered death by decapitation con- 

 tained about O'TY of a grain. 1 



The action of pneumic acid upon the bicarbonates in the 

 blood is exemplified in a marked manner by certain experi- 

 ments of Bernard. When bicarbonate of soda is injected 

 into the jugular of a living animal, a rabbit, for example, it 

 is decomposed as fast as it gets to the lungs, and carbonic 

 acid is evolved. This experiment produces no inconvenience 

 to the animal when the bicarbonate is introduced slowly ; but 

 when it is injected in too great quantity, the evolution 

 of gas in the lungs is so great as to fill the pulmonary struc- 

 ture and even the heart and great vessels, and death is the 

 result. 2 



Exhalation of Watery Vapor. The fact that the expired 

 air contains a considerable quantity of watery vapor has long 

 been recognized ; and most of the earlier experimenters who 

 directed their attention to the phenomena of respiration 

 made the estimation of the quantity exhaled, and the laws 

 which regulate pulmonary transpiration, the subject of in- 

 vestigation. It is evident that there must be many cir- 

 cumstances materially influencing this process, such as the 

 hygrometric condition of the atmosphere, temperature, ex- 

 tent of respiratory surface, etc., which are of sufficient impor- 

 tance to demand special consideration. In many points of 

 view, also, it is interesting to know the absolute quantity of 

 exhalation from the lungs. 



1 ROBIN and VERDEIL, Chimie Anatomique et Physiologique, Paris, 1853, tome 

 ii., p. 460. 



2 Op. cit., tome i., p. 165. These experiments referred to the decomposition of 

 cyanide of potassium in the lungs, as well as bicarbonate of soda. They were 

 published in the Archives Generates in 1848, before the discovery of pneumic 

 acid, and Bernard expressed surprise that the two substances experimented upon, 

 which required an acid for their decomposition, should be decomposed in an al- 

 kaline fluid like the blood. Though made without a knowledge of the existence 

 of pneumic acid, the observations none the less illustrated its physiological 

 action. 



