98 GASES OF THE BLOOD. 



This then is an example of the change produced in the 

 blood by its passage through a special excretory organ. But 

 all parts of the body, bones, muscles, nerves, etc., must 

 act on the blood as it passes through them, and leave in it 

 some mark of their action, too slight though it may be, 

 at any given moment, for analysis by means now at our 

 disposal. 



On the Gases contained in the Blood. 



The gases contained in the blood are carbonic acid ; 

 oxygen, and nitrogen, 100 volumes of blood containing 

 from 40 to 50 volumes of these gases collectively. 



Arterial blood contains relatively more oxygen and less 

 carbonic acid than venous. But the absolute quantity of 

 carbonic acid is in both kinds of blood greater than that of 

 the oxygen. The proportion of nitrogen is in both very small. 



Concerning the manner in which carbonic acid and 

 oxygen exist in the blood, considerable uncertainty still 

 prevails. It is most probable that they are partly free, 

 and partly in a state of weak chemical combination. That 

 portion of the carbonic acid which is chemically combined, 

 is contained partly in a bicarbonate of soda, and partly is 

 united with phosphate of the same base. The oxygen is 

 carried in the red corpuscles. 



That the oxygen is absorbed chiefly by the red corpuscles 

 is proved by the fact that the serum alone has little or no 

 more power of absorbing this gas than pure water ; and 

 the observations of Professor Stokes, before referred to, 

 make it likely that the colouring matter, or cruorin, is the 

 constituent of the cells which thus holds the oxygen in weak 

 chemical union with itself, to deliver it up as it is wanted 

 in the course of the circulation. 



Blood Crystals. 



When blood has been at rest for some time, either within 

 or without the body, and especially if diluted with water, 

 crystals of various kinds not unfrequently form in it. 



