44 IMMEDIATE PKINCIPLES OP THE TISSUES. 



gas is formed in the alimentary canal ; but precisely how, is not 

 ascertained. There is also a very small quantity of it in the gases 

 expired in normal respiration. None has, however, yet been found 

 in the blood, though the last fact might lead us to expect to find 

 it there. 1 



3. Nitrogen. (N.) 



Free nitrogen is found in the air-cells of the lungs, in the blood, 

 and the intestinal gases, both healthy and morbid. The whole 

 amount in the lungs and the blood varies from 46.755 to 47.52 

 grains. In the blood It is dissolved and in a fluid state. It consti- 

 tutes from one- tenth to one-sixth of all the gases in this fluid, and 

 is more abundant in the arterial than in the venous blood (as 1.51 

 to 1). Animals suffering from emaciation inhale more nitrogen 

 from the atmosphere than' they return to it by expiration. 



4. Carbonic Acid. (CO. 2 ) 



This gas exists in the lungs, the alimentary canal, the blood, and 

 the urine, 2 it being in the two latter in a state of solution. The 

 amount in the blood would, in its gaseous state, occupy from one- 

 fifth to one-third of the space actually filled by the whole mass of 

 blood. It is dissolved in both the serum of the blood and the cor- 

 ) puscles, there being more in arterial than in venous blood (R. and. 

 V.\ as is the case with oxygen and nitrogen. Oxygen is, however, 

 dissolved principally in the corpuscles, as has been seen. The 

 greater amount of carbonic acid gas in the arterial blood confirms 

 the idea that it is set free in the lungs from the carbonates in the 

 blood by the action upon the latter of pneum^c acid. (Robin and 

 Verdeil) That it is originally formed, however, by the action of 



1 Carburetted and sulphuretted hydrogen are also included among the immediate 

 principles by Robin and Verdeil. They are here omitted, since they are found only 

 in the air-passages and the large intestine, and appear to be evolved in consequence 

 of some abnormal chemical process. In the intestine the sulphuretted hydrogen is 

 always in smaller quantity than the other gases. It is formed in the alimentary 

 canal ; but precisely how, is not ascertained. It is also disengaged from abscesses 

 near a mucous membrane (e. g. near the anus), or by putrefaction of pus or of or- 

 ganized tissue. Abscesses on the limbs, under the deltoid, or hi the kidneys, have 

 also been known to disengage it. 



2 "All the tissues in the body contain a small quantity of dissolved gases, and 

 carbonic acid can be detected in all the animal fluids, &c." Todd and Bowman, 

 p. 730, Am. ed. 



