ACTION OF THE KIDNEYS. 643 



to see how these substances get into the circulation, as no trace 

 of them can be found in the blood. The heat generated is pro- 

 portional to the food digested. In hot climates, the waste of heat 

 being small, but little food is required, whereas in cold climates 

 the waste of heat is great, and hence the appetite is greatly in- 

 creased. Liebig conceives that, in consequence of the coldness 

 of the atmosphere in frigid climates, a greater proportion of oxy- 

 gen is inhaled than in hot climates ; but as the air inhaled is heat- 

 ed in the lungs to 98, and as the azotic gas constitutes four- 

 fifths of this air, one would expect that the heat necessary to 

 heat this azotic gas from a very low temperature to 98 p , would 

 fully compensate for any increase in the density of the oxygen 

 gas. The number of respirations per minute ought to increase 

 in cold climates, or, what is more probable, the per centage of 

 carbonic acid evolved, and of oxygen absorbed during each res- 

 piration ought to increase. 



We want additional experiments. The statement given in 

 this chapter applies only to the summer. I am not aware of any 

 attempt to determine the carbonic acid formed by respiration 

 during winter. It would be interesting to know the per centage 

 of carbonic acid given out by breathing in India and in St 

 Petersburg or Stockholm. The subject is well worth the atten- 

 tion of men of science in India. 



CHAPTER III. 



OF THE ACTION OF THE KIDNEYS. 



A VERY great proportion of blood passes through the kid- 

 neys ; indeed, we have every reason to conclude that the whole 

 of the blood passes through them very frequently. These or- 

 gans separate the urine from the blood, to be afterwards evacua- 

 ted without being applied to any purpose useful to the animal. 



The kidneys are absolutely necessary for the continuance of 

 the life of the animal ; for it dies speedily when they become by 

 disease unfit to perform their functions : therefore the change 

 which they produce in the blood is a change necessary for qua- 

 lifying it to answer the purposes for which it is intended. 



In a preceding chapter of this work, a very minute account 



