157 



cubic inch, or ~r P a , rt f their bulk **. Dr Bostock, 

 on the other hand, concludes, that the air, by a 

 single respiration, loses only -^ part of its bulk t 

 Amid such contradictory results, it is not to be ex- 

 pected that a conclusion can be drawn which shall 

 truly express the amount of the diminution in que- 

 stion : and indeed, from a consideration of the 

 powers which govern respiration, and the various 

 circumstances which sensibly affect that process, we 

 cannot but consider the actual loss of bulk which 

 the air suffers by a single respiration, as in its nature 

 extremely difficult, if not impossible, to determine. 

 All, therefore, that we can at present venture to as- 

 sert, is, that the difference between the volumes of 

 air inspired and expired, in natural respiration, is ex- 

 tremely small : and to this we may add our belief, 

 that the necessary loss of bulk which oxygen gas 

 suffers, by its conversion into carbonic acid, in that 

 process, may be made sufficient to account for it. 



126. Several attempts have been made to ascer- 

 tain the absolute quantity of oxygen gas consumed 

 in a given time by respiration : but many circum- 

 stances concur to render this a matter of very diffi- 

 cult determination. Dr Menzies, from his experi- 

 ments, was led to conclude, that, in respiration, 36 

 cubic inches of oxygen gas were, every minute, con- 

 verted into carbonic acid ; and that thus 51840 cu- 

 bic inches of that gas, equal to 17625.6 grains, were 



* Researches, p. 433. 



t Essay on Respiration, p. 99210. 



