130 



CIRCULATING FLUIDS: 



Supposing that adults sleep seven and cliildren nine hours 

 per day, the amount of carbon consumed is on an average — 



It is thus evident that the quantity of carbonic acid ex- 

 pired is very variable, and that it may be altered by many 

 circumstances. Hunger and rest diminish, satiety and labour 

 increase it. It is greater during the day than the night, in 

 the proportion of 1'237 to one. If the expired carbonic acid 

 be estimated in relation to the weight of the bod}^, it is found 

 that children give off a proportionally greater amount of this 

 gas than adults. In some forms of disease, the amount of 

 expired carbonic acid falls below the standard ; it seems, in a 

 state of health, to vary directly with the acti\dty of the circu- 

 lation. 



The influence of muscular activity on the amount of carbon 

 consumed, has been clearly shown by some experiments made 

 by Dr. Hofmann during a pedestrian toiir. His diet was simple 

 and scanty, he took no drink, walked during the Avhole day, 

 weighed all his food and every excretion that could be Aveighed 

 (even the nasal mucus), as well as himself; he then found that 

 the weight lost by the body was never equalled by the excess 

 of the excrements over the food, and that there was a constant 

 loss of matter by the skin and lungs, which amounted to more 

 than 1 lb. We must pass over the details of his experiments. 

 Brunner and Valentin found that the weight of carbon they 

 consumed per hour varied from 134 to 170 grains, and averaged 

 160. The volume of expired carbonic acid per hour, on an 



