352 RESPIRATION. 



reaches the proportion of about 420 : 200, when the great quantity 

 of oxygen must necessarily be employed for the oxidation of the 

 hydrogen. This ratio becomes subsequently so changed (being 

 300 : 100, or even 270 : 100) that the oxygen is scarcely suffi- 

 cient for the formation of carbonic acid. This lower ratio then 

 remains tolerably constant. 



It would appear from the extensive investigations of Regnault 

 and Reiset, that there exists almost one uniform ratio for the most 

 different animals in respect to the composition of the air which is 

 expired during fasting. The consumption of oxygen is invariably 

 less in fasting than in well-fed animals ; thus, for instance, 

 1000 grammes' weight of rabbits, which when fasting absorbed on 

 an average only 0*749 of a gramme of oxygen, took up when well 

 fed as much as 0*877 of a gramme. A much smaller quantity of the 

 absorbed oxygen reappears in the carbonic acid when animals are 

 fasting than when they are abundantly fed upon amylaceous sub- 

 stances. Thus, for instance, in rabbits fed upon carrots, from 

 84 to 95^ of the absorbed oxygen were expended in the formation 

 of carbonic acid, while only from 7^*2 to 70*7^ were consumed 

 in this manner when the animals were fasting. Regnault and 

 Reiset frequently observed an absorption of nitrogen by animals 

 during fasting ; this being almost invariably the case with birds, 

 but of rarer occurrence in mammals. 



Bidder and Schmidt* have made two admirable series of 

 experiments on the respiration of cats, when these animals were 

 entirely deprived of solid food. A cat weighing 2464 grammes 

 exhaled 699*52 grammes of carbonic acid (= 190*78 grammes of 

 carbon) and 525*67 grammes of aqueous vapour during 18 days' 

 inanition. A quantitative determination and analysis of the other 

 excretions showed that here, almost exactly as in the case of 

 Regnault and Reiset's direct observations, only 76*5 grammes of 

 every 100 parts of the oxygen absorbed during inanition were 

 eliminated with the expired carbonic acid; and further, that 

 75*15 parts of aqueous vapour were exhaled with 100 parts of 

 carbonic acid (the animals were very rarely permitted to drink 

 water), whilst 41'72-g- of the water exhaled were eliminated by 

 perspiration. When we compare the observations made on indi- 

 vidual days during this series of experiments, we obtain the follow- 

 ing results : the absorption of oxygen decreases constantly to the 

 death of the animal, at first very rapidly (about 2 grammes in the 

 24 hours during the first few days), and then more slowly and 

 * Op. cit. pp. 304 et 340. 



