274 ITS BEARING ON MEDICAL PRACTICE. 



Regnault directed liis attention especially to the distribution of the 

 oxyft'eu absorbed by animals, between the carbon and hydrogeD of their 

 blood or tissues, which had been laid down by Lavoisier in the propor- 

 tion of 81 to 19. He found that the proportion was not a fixed one, but 

 varied with the food in a very instructive manuer. 



The average of his experiments on fourteen aniuials, including worms, 

 lizards, and insects, as well as birds and mammals, was — 



Oxygen combined with carbon 81. 7 



Oxygen combined with hydrogen. 19. 3 



a result nearly identical with that found by Lavoisier. The highest 

 proportion of oxygen combined with hydrogen occurred in the case of 

 chickens fed on meat, and amounted to 32 per cent.; and the lowest 

 ])roportion occurred in the case of rabbits fed on bread and oats, and 

 amounted to 1 per cent. only. 



Still more recent experiments, made with improved apparatus and 

 methods by Pettenkofer and Voit, in Munich, show, like those of Reg- 

 nault, that the proportion of the oxygen employed in forming carbonic 

 acid to the whole oxygen absorbed varies with the food, ranging in the 

 case of a large dog from 52.4 to 148.2, according as the animal was kept 

 altogether without food, or fed upon a mixed diet of meat and sugar. 

 These investigations have also shown that, under ordinary conditions, 

 it is probable that a dog consumes nearly all the oxygen absorbed in 

 the formation of carbonic acid. 



Before leaving the subject of animal heat, it is worth while to estimate 

 its amount in a manner that will bring it into comparison with ordinary 

 mechanical work. 



In Lavoisier's experiment with the Guinea pig, 402.27 grams of ice 

 were melted in ten hours; from this fact we find, assuming the latent 

 heat of ice at 142° F., and 772 as Joule's coefficient for converting Brit- 

 ish heat-imits into foot pounds, 



Mechanical icorlc-equivalent to the daily animal heat of Lavoisier'' s Guinea 

 2ng = 



402.27 X 24 X 142 x 15.432 x 772 oooom i- ^^ i 

 TOOinno ^ ^^^"^'^ foot-pounds. 



As the average weight of a Guinea pig is four joounds, the preceding 

 amount of work, representing animal heat, would be suflScient to raise 

 the weight of the animal through a vertical height of — 



233310 ^ , ^^ ., 

 4 X 5280 



Eanke has shown, by experiments made upon himself, under various 

 conditions of food and fasting, by means of Pettenkofer and Voit's appa- 

 ratus, that his daily excretion of carbonic acid varied from 6G0 grams to 

 860 grams, showing a mean of 760 grams. His weight was 67 kilograms, 

 from which fact, and the assumption that an English mile is 1,600 meters, 

 we obtain, employing the constants already given, the height through 



