CONSUMPTION OF OXYGEN. 417 



oxygen consumed under various physiological conditions, they 

 are not to be compared with the more recent observations, 

 particularly those of Kegnault and Reiset, Yalentin and Brun- 

 ner, Dumas, Andral and Gavarret, Scharling, and Edward 

 Smith, with regard to the absolute quantity of oxygen made 

 use of in respiration. In the observations of Regnault 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 carefully esti- 

 mated. In most of the experiments, the confinement did not 

 appear to interfere 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 infinitely 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 function. This is known as 

 the direct method of investigating the changes in the air pro- 

 duced by respiration. As employed by Regnault and Reiset, 

 it is only adapted to experiments on animals of small size. 

 These give but an approximative idea of the processes as they 

 take place in the human subject, as it is natural to suppose 

 that the relative quantities of gases consumed and produced 

 in respiration vary in different orders of animals. 1 



1 In Robin's Journal de V Anatomic et de la Phytiologie, July, 1864, tome i., 

 p. 429, we find an analysis of researches on respiration by Dr. Max Pettenkofer, in 

 which the conditions for accurate observations on the human subject seem to be 

 fulfilled. Dr. Pettenkofer has constructed a chamber large enough to admit a man, 

 and allow perfect freedom of motion, eating, sleeping, etc., into which air is con- 

 stantly introduced in definite quantity, and from which the products of respiration 

 are constantly removed, and estimated. An incomplete series of observations is 

 published, which has particular reference to the products of respiration. Thus 

 far the subject of consumption of oxygen has not been considered. Extended ob- 

 servations by Dr. Pettenkofer will undoubtedly settle many disputed questions 

 regarding the changes of the air in respiration. This method was adapted to the 

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