BLOOD. 135 



Volumes in cubic centimeters. Gas, r 7'0 CO.j 



Arterial blood of the calf . . 108 . yielded 12-6 -j 3-0 O 



2-6 N 

 I 10-2 CO., 

 Venous blood of the same calf . 153 . . . 13'i 



1-8 

 1-3 N 



61 COj 



Ditto 140 . . . 7-7-I l-OO 



0-6 N 



From these experiments^ it follows, 1st, that carbonic acid, 

 oxygen, and nitrogen exist both in arterial and in venous blood ; 

 and, 2dly, that the quantity of oxygen is greater, and the quan- 

 tity of carbonic acid less in arterial than in venous blood, a fact 

 which confirms the opinion we have expressed regarding the 

 formation of carbonic acid and the theory of respiration generally. 



The bright coloiu* which is communicated to the blood by 

 oxygen, as well as the dark shade that is induced by the trans- 

 mission of carbonic acid through it, are the actual shades of 

 colour that we see in arterial and venous blood. Moreover, 

 when blood has been rendered artificially venous in this way, 

 it may be rendered arterial in its colour by agitation with a 

 certain quantity of oxygen, and we can then obtain from it a 

 mixture of oxj'gen and carbonic acid. 



We have now enumerated the most interesting phenomena 

 in reference to the expired air. We have ab'cady noticed the 

 circumstance that nitrogen is expu'ed. It follows natiu-ally 

 that this gas, which forms the principal constituent of the 

 atmosphere, should be inhaled; and, according to Edwards, 

 there is a sort of compensation between the amount of exhaled 

 and inspired nitrogen, so that the quantity of this gas in the 

 atmosphere remains fixed, the amount of expired nitrogen pre- 

 dominating at one time, and of inspired nitrogen at another. 

 According to Berzelius, the portion of nitrogen taken up by 

 the blood is only changed when the blood comes in contact 

 with a gas which either contains no nitrogen or which possesses 

 it in a greater ratio than atmospheric air. Nitrogen is there- 

 fore evolved from the blood during the inspiration of oxygen 

 or hydrogen, and the circulating fluid is then found to contain 

 a greater proportion than usual of oxygen or hydi'ogen ; but if 

 nitrogen is inhaled, an excess of this gas is found in the blood, 

 while oxygen and carbonic acid are evolved in accordance with 

 the known law of the diffusion of gases. 



