EFFECT OF RESPIRATION ON THE BLOOD. 169 



the amount of water is calculated from Seguin's experiments, but it ap- 

 pears from these results, which are obtained by a much more accurate 

 process, that the number there given is undoubtedly too high. 



The time of exposure of the blood to the air is only a second or two. 

 The color changes, as has been described before, from blue to crimson, 

 and the temperature rises a degree or two, as is shown by an examina- 

 tion of the left cavities of the heart. The water thus removed is not 

 pure, but contains animal matter in a state of decay. 



Though we have treated of the act of respiration as consisting of two 

 separate and consecutive stages, inspiration and expiration, Respiration is 

 in reality it proceeds continuously. At the respiratory sur- 

 face, which is the wall of the air-cell, the passage of oxygen ing. 

 inward, and of carbonic acid and steam outward, takes place in a steady 

 and unvarying manner. The periodicity under which it has been conven- 

 ient to speak of this function concerns only the introduction and removal 

 of gases from the large air-ways. 



Considering, therefore, the continuous loss of water which the venous 

 blood brought by the pulmonary arterial branches undergoes, Effect of respi- 

 it must give rise necessarily to a greater density in the blood 

 on the left side as compared with that of the right side of blood, 

 the heart. The total quantity of blood passing through the lungs in one 

 minute is 225 ounces, and the loss of water from this in the same time 

 can not be more than 7 grains. This, therefore, shows that the actual 

 loss of water by the blood during its passage over the air-cells is about 

 15 ^ QO part, a quantity which is altogether inappreciable, so far as its in- 

 fluence on the specific gravity is concerned, and showing us that the ob- 

 servations which some experimenters have made on this point, with a 

 view of demonstrating an increased spissitude, density, or cohesiveness 

 of the blood on the left side of the heart, from the giving up of its water 

 as it passed through the respiratory organ, are either exaggerated or af- 

 fected by some deceptive cause. 



The introduction of an irrespirable gas into the lungs, or the prevention 

 of the access of the atmosphere, brings the circulation of the Effect of the in- 

 blood to a stop ; for that movement depends, as I have shown, 

 on the aeration taking place in the pulmonary capillaries. In gases. 

 such cases there will be an engorgement of the right heart and vessels 

 arising therefrom, but, if the stoppage has not lasted too long, the current 

 may be re-established by re-establishing the respiration. Death com- 

 monly ensues on an exclusion of the air for five minutes, and, in cases 

 of drowning, it is rare for restoration to be effected if the immersion has 

 lasted more than four. 



In the respiration of protoxide of nitrogen, a gas which is an energetic 

 supporter of combustion, and acting more powerfully on the animal sys- 



