180 RESPIKATIOX. 



rise to this change, the conditions capable of effecting it inde- 

 pendent of respiration, and some other differences between 

 arterial and venous blood, were discussed in the chapter on 

 Blood, p. 77): 2d, and in connection with the preceding 

 change, it gains oxygen; 3d, it loses carbonic acid; 4th, it be- 

 comes 1 or 2 F. warmer; 5th, it coagulates sooner and more 

 firmly, and, apparently, contains more fibrin. 



The oxygen absorbed into the blood from the atmospheric 

 air in the lungs is combined chemically with the haemoglobin 

 of the red blood-corpuscles. In this condition it is carried in 

 the arterial blood to the various parts of the body, and with it 

 is, in the capillary system of vessels, brought into near relation 

 or contact with the elementary parts of the tissues. Herein, 

 co-operating probably in the process of nutrition, or in the re- 

 moval of disintegrated parts of the tissues, a certain portion of 

 the oxygen which the arterial blood contains disappears, and 

 a proportionate quantity of carbonic acid and water is formed. 



But it is not alone in the disintegrating processes to which 

 all parts of the body are liable, that oxygen is consumed and 

 carbonic acid and water are formed in its consumption. A 

 like process occurs in the blood itself, independently of the 

 decay of the tissues; for on the continuance of such chemical 

 processes depend, directly or indirectly, not only the tempera- 

 ture of the body, but all the forces, the nervous, the muscular, 

 and others, manifested by the living organism. 



The venous blood, containing the new-formed carbonic acid, 

 returns to the lungs, where a portion of the carbonic acid is 

 exhaled, and a fresh supply of oxygen is again taken in. 



Mechanism of Various Respiratory Actions. 



It will be well here, perhaps, to explain some respiratory 

 acts, which appear at first sight somewhat complicated, but 

 cease to be so when the mechanism by which they are per- 

 formed is clearly understood. The accompanying diagram 

 (Fig. 65) shows that the cavity of the chest is separated from 

 that of the abdomen by the diaphragm, which, when acting, 

 will lessen its curve, and thus descending, will push downwards 

 and forwards the abdominal viscera; while the abdominal 

 muscles have the opposite effect, and in acting will push the 

 viscera upwards and backward, and with them the diaphragm, 

 supposing its ascent to be not from any cause interfered with. 

 From the same diagram it will be seen that the lungs commu- 

 nicate with the exterior of the body through the glottis, and 

 further on through the mouth and nostrils through either of 

 them separately, or through both at the same time, according 



