CONSUMPTION OF OXYGEN. 141 



made to respire for a time pure oxygen. Although this is the gas which is essential in 

 ordinary respiration, the process being carried on about as well in a mixture of oxygen 

 with hydrogen as with nitrogen, the functions do not seem to be much altered when the 

 pure gas is taken into the lungs. Allen and Pepys confined animals for twenty -four 

 hours in an atmosphere of pure oxygen without any notable results ; but, as is justly 

 remarked by Longet, these experiments do not show that it would be possible to respire 

 unmixed oxygen indefinitely without inconvenience. As it exists in the air, oxygen is 

 undoubtedly in the best form for the permanent maintenance of the respiratory func- 

 tion. The blood seems to have a certain capacity for the absorption of oxygen, which is 

 not increased when the pure gas is respired. 



The only other gas which has the power of maintaining respiration, even for a time, 

 is nitrous oxide. This is absorbed by the blood-corpuscles with great avidity, and, for a 

 time, it produces an exaggeration of the vital processes, with delirium, etc. properties 

 which have given it the common name of the laughing gas ; but this condition is fol- 

 lowed by anaesthesia, and finally asphyxia, probably because the gas has such an affinity 

 for the blood-corpuscles as to remain to a certain extent fixed, interfering with that inter- 

 change of gases which is essential to life. Notwithstanding this, experimenters have 

 confined with impunity rabbits and other animals in an atmosphere of nitrous oxide for 

 a number of hours. In all cases they became asphyxiated, but in some instances were 

 restored on being brought again into the ordinary atmosphere. 



Other gases which may be introduced into the lungs either produce asphyxia, nega- 

 tively, from the fact they are not absorbed by the blood and are incapable of carrying on 

 respiration, like hydrogen or nitrogen, or positively, by a poisonous effect on the system. 

 The most important of the gases which act as poisons are, carbonic oxide, sulphuretted 

 hydrogen, and arseniuretted hydrogen. It is somewhat uncertain whether carbonic acid 

 exert its deleterious influence as a poison or as merely taking the place of the oxygen in 

 the blood-corpuscles. It is easily displaced from the blood by oxygen, and therefore 

 does not seem to possess the properties of a poison, like carbonic oxide and some other 

 gases, which become fixed in the blood and are not readily displaced when fresh air is 

 introduced into the lungs. 



Consumption of Oxygen. The determination of the quantity of oxygen which is re- 

 moved from the air by the process of respiration is a question of great physiological 

 interest and one which engaged largely the attention of Lavoisier and those who have 

 followed in his line of observation. On this point, there is an accumulated mass of 

 observations, which are comparatively unimportant from the fact that they were made 

 before the means of analysis of the gases were as perfect as they now are. Although 

 many of the results obtained by the older experimenters are interesting and instructive 

 as showing the comparative quantities of oxygen consumed under various physiological 

 conditions, they are not to be compared with the more recent observations. In the 

 observations of Eegnault and Reiset, the animal to be experimented upon was enclosed 

 in a receiver filled with air, a measured quantity of oxygen was introduced as fast as it 

 was consumed by respiration, and the carbonic acid was constantly removed and care- 

 fully estimated. In most of the experiments, the confinement did not appear to inter- 

 fere with the functions of the animal, which ate and drank in the apparatus and was in 

 as good condition at the termination as at the beginning of the observation. This method 

 is much more accurate than that of simply causing an animal to breathe in a confined 

 space, when the consumption of oxygen and ' accumulation of carbonic acid and other 

 matters must interfere more or less with the proper performance of the respiratory func- 

 tion. As employed by Eegnault and Reiset, it is only adapted to experiments on animals 

 of small size. These give but an approximate idea of the processes as they take place in 

 the human subject, as it is natural to suppose that the relative quantities of gases con- 

 sumed and produced in respiration vary in different orders of animals. 



