EXHALATION OF CARBON DIOXIDE. 147 



carbon dioxide exhaled. It has already been stated that -^ to -fo (T4 to 2 per 

 cent.) of the inspired air is lost in the lungs ; or it may be said in general 

 terms, that the oxygen absorbed is equal to about five per cent, of -the volume 

 of air inspired, and the carbon dioxide exhaled, only about four per cent. A 

 part of the deficiency in volume of the expired air is to be accounted for, 

 then, by a deficiency in the exhalation of carbon dioxide. 



The experiments of Regnault and Reiset have an important bearing on 

 the question under consideration. As these observers were able to accurately 

 measure the entire quantities of oxygen consumed and carbon dioxide pro- 

 duced in a given time, the relation between the two gases was kept constantly 

 in view. They found great variations in this relation, mainly dependent upon 

 the regimen of the animal. The total loss of oxygen was found to be much 

 greater in carnivorous than in herbivorous animals; and in animals that 

 could be subjected to a mixed diet, by regulating the food this was made to 

 vary between the two extremes. The mean of seven experiments on dogs 

 showed that for every 1,000 parts of oxygen consumed, 745 parts were exhaled 

 in the form of carbon dioxide. In six experiments on rabbits, the mean was 

 919 for every 1,000 parts of oxygen. 



In animals fed on grains, the proportion of carbon dioxide exhaled was 

 greatest, sometimes passing a little beyond the volume of oxygen consumed. 



" The relation is nearly constant for animals of the same species which are 

 subjected to a perfectly uniform alimentation, as is easy to realize as regards 

 dogs ; but it varies notably in animals of the same species, and in the same 

 animal, submitted to the same regimen, but in which we can not regulate the 

 alimentation, as in fowls." 



When herbivorous animals were entirely deprived of food, the relation 

 between the gases was the same as in carnivorous animals. 



The final result of the experiments of Regnault and Reiset was that the 

 " relation between the oxygen contained in the carbon dioxide and the total 

 oxygen consumed, varies, in the same animal, between 0-62 and 1-04, accord- 

 ing to the regimen to which it is subjected." These observations on animals 

 have been confirmed in the human subject by Doyere, who found a great 

 variation in the relations of the two gases in respiration ; the volume of 

 carbon dioxide exhaled varying between 0-862 and 1-087 for 1 part of oxygen 

 consumed. 



As regards the destination of the oxygen which is not represented in the 

 carbon dioxide exhaled, it is certain that a part of it, at least, unites with 

 hydrogen to form water, this contributing to the production of animal heat y 

 a question that will be fully discussed in another connection. 



The variations in the relative volumes of oxygen consumed and carbon 

 dioxide produced in respiration are not favorable to the hypothesis that the 

 carbon dioxide is always a result of the direct action of oxygen upon the car- 

 bohydrates and fats. Such a definite relation between these two gases can 

 not be assumed to exist, in view of the fact that carbon dioxide may be given 

 off by the tissues in the absence of oxygen. 



Many of the points that have been considered with relation to the varia- 



