APPARATUS FOE PHYSIOLOGICAL USE. 263 



used up at once as it is in a furnace or is it stored up in the 

 tissues and given off afterwards ? For instance, do I use up 

 the oxygen that I get when I draw a breath immediately 

 in keeping up muscular movements, or do I store up either 

 the whole or a part of it in my muscles for use afterwards ? 

 This question is not to be answered by means of the air- 

 pump which we have now been considering, but by another 

 piece of apparatus which I now show you here, that of 

 Pettenkofer and Voit, for estimating the amount of car- 

 bonic acid given off and of oxygen used up by any man or 

 animal in a given time. Although this seems very large, 

 it is really a very small apparatus of its kind. Pettenkofer 

 and Voit have an enormous apparatus at Munich in which 



FIG. 



>. Diagram of Volt's apparatus. The letters indicate the same parts as in 

 figure 5. 



they can estimate the amount of carbonic acid given off 

 and the oxygen used by a man. Here we can only use a 

 small animal such as a rabbit (No. 3787 in Catalogue, third 

 edition). 



Now, complicated as this apparatus seems, it is in reality 

 very simple in its plan. Here we have a glass box, and in 

 it a rabbit. The box is rather small for the animal, and if 

 it were completely shut, the box would very soon begin to 

 feel very close, and the animal very uncomfortable, so, in 

 order to prevent this, we must have a stream of air passing 

 through it. 



It is very difficult to analyse large quantities of air, and 



