CHANGES IN THE BLOOD BY RESPIRATION. 295 



oxygen or atmospheric air, at once assumes the arterial tint, although 

 its carbonic acid may remain. According to Pfliiger's experiments, if 

 defibrinated dog's blood be placed in two flasks, and shaken up, one with 

 pure oxygen, the other with a mixture of oxygen and carbonic acid, both 

 specimens will present the same bright color ; both of them being found 

 on analysis to contain nearly the same quantities of oxygen, while their 

 proportions of carbonic acid are very different. Also the recently drawn 

 blood of these animals, after they have been made to breathe either pure 

 oxygen, or oxygen and carbonic acid mingled, is of the same color in 

 each instance ; the percentage of oxygen which it contains being the 

 same, but that of carbonic acid being different in the two cases. 



It is the oxygen, therefore, which, on being taken up by the blood- 

 globules, changes their color from dark purple to bright red. It passes 

 off with the arterial blood in this condition, and is then distributed to 

 the capillary circulation. Here, as the blood comes in contact with the 

 tissues, its oxygen in great measure disappears, and its color is again 

 changed from arterial to venous. 



The loss of oxj^gen by the blood, in traversing the capillaries, is due 

 to its transfer from the blood-globules to the substance of the tissues. 

 Nearly all the tissues, in fact, exert an absorbent power upon oxygen, 

 when exposed to this gas or to atmospheric air containing it. The ex- 

 periments of Paul Bert 1 have shown that the following tissues, extracted 

 from the body of the recently killed dog and exposed to the contact of 

 atmospheric air in closed vessels, absorb oxygen, with different degrees 

 of intensity, in the following order, namely : muscles, brain, kidneys, 

 spleen, testicle, and pounded bones. Of these the muscles are the most 

 active, absorbing 50 cubic centimetres of oxygen for every 100 grammes 

 of muscular tissue; while the bones absorb only a little over Jt cubic 

 centimetres for the same weight of substance. 



The tissues have even a greater absorbent power for oxygen than the 

 blood-globules themselves. This is shown by the experiments of Spal- 

 lanzani, and still more completely by those of Bert. In these experi- 

 ments, three equal portions of recently drawn defibrinated dog's blood 

 are placed in test-tubes, a piece of fresh muscular tissue from the same 

 animal being introduced into one of them, a portion of the spleen-tissue 

 into another, while the third is left to itself. After a time it is found 

 that the solid tissues have abstracted oxygen from the blood with which 

 they are in contact, so that in these two specimens the blood, on 

 analysis, contains less oxygen than in the third specimen, which has 

 remained by itself. The result obtained by Bert was as follows : 



QUANTITY OF OXYGEN BY VOLUME REMAINING IN 



Blood left to itself 18 per cent. 



Blood containing spleen tissue . . 12 " 



Blood containing muscular tissue 6 " 



1 Lecjons sur la Physiologic compare de la Respiration. Paris, 1870, p. 46. 



