70 BIOLOGY. [BOOK r. 



afterwards, exciting one of its nerves by an electric current, we 

 contract the muscle, immediately a certain consumption of 

 oxygen responds to the contraction ; in the passage the globules 

 are charged with carbonic acid ; they grow black ; they become 

 venous. Analogous phenomena are observed for the same reason 

 during the hibernal sleep, during syncope ; and the case must be 

 the same for the blood traversing the veins during dreamless 

 slumber. 



Claude Bernard has shown that we can produce at will the 

 changes of coloration in the blood by the section and the excita- 

 tion of certain nerves. 



Essentially in all these special cases of organic atony, there is 

 a general phenomenon : the inaction or the diminished action of 

 the tissues, and of the organs; hence the superabundance of 

 oxygen in the blood. We see therefore that in a certain sense 

 we only need to determine the absorption of oxygen by a tissue 

 to measure the degree of its functional activity. 



The exchange of gas between the tissues and the globules 

 is probably accomplished by osmosis and diffusion. We must 

 nevertheless remark that in all likelihood the oxygen is in the 

 state of combination with the substance of the globule and the 

 hsematoglobuline. In effect, an organic acid, the pyrogallic acid, 

 which is greedy of oxygen, and absorbs it with special ease and 

 eagerness when it is in solution in the alkaline liquids, succeeds 

 not however in despoiling thereof the globules of the blood. 

 These globules indeed have for oxygen such affinity, that in the 

 arterial blood they absorb it almost in totality, and rob thereof 

 almost completely the plasma. Like all chemical phenomena, the 

 combination of the globules and of the oxygen is influenced by 

 the temperature. At a low temperature it ceases to be accom- 

 plished : for instance in the body grown cold of a mammifer 

 in the state of hibernal sleep. On the contrary, when the 

 temperature rises, the fixation of the oxygen becomes easy, 

 proceeding as far as 40 to 45 degrees. [Centigrade scale.] 

 Beyond that point the oxydation of the globules tends to 



