232 PHYSIOLOGICAL CHEMISTRY. 



abundant nitrogen must exist in a condition of simple solution. 

 The methods of accurate gas analysis as applied to blood were 

 developed by Lothar Meyer, who made a number of deter- 

 minations in blood from different sources. These methods 

 have been further improved by others who have placed many 

 results on record. 



The mean amount of nitrogen is about 2 volume per cent. 

 The oxygen and carbon dioxide are variable. In arterial 

 blood the oxygen, which is held mainly through the agency 

 of hemoglobin, amounts to about 22 per cent by volume ; that 

 is, from 100 cc. of arterial blood 22 cc. of oxygen in the mean 

 may be obtained by aid of the vacuum pump. The venous 

 blood always contains less oxygen, probably not over 15 per 

 cent by volume. These amounts are far larger than could be 

 absorbed from the air through the partial pressure of the oxy- 

 gen present. In fact it may be shown that only a fraction of 

 i volume per cent may be held by the blood plasma perfectly 

 free from corpuscles. 



The loosely combined carbon dioxide may vary from 30 to 

 40 volume per cent in the arterial blood, while in venous blood 

 it is much higher, reaching nearly 50 volume per cent in the 

 mean. This gas is held partly in the form of bicarbonate and 

 partly through the agency of the proteins, especially the hemo- 

 globin. Most of the carbon dioxide is, however, held by the 

 serum and may be largely drawn out by aid of the vacuum 

 pump. On withdrawal of the gas other weak acid bodies are 

 able to take its place in alkali combination. It is held by some 

 observers that the globulins have this power. In acid intoxi- 

 cations where mineral or organic acids increase in the blood 

 the carbon dioxide rapidly decreases and may fall to a tenth or 

 twentieth even of its usual value. These stronger acids take 

 the alkali and there is therefore nothing left to hold the carbon 

 dioxide. 



Some of these points will be taken up in a later chapter in 

 discussing respiration phenomena. 



Other Substances. Besides the substances mentioned 



