120 ANATOMY AND PHYSIOLOGY. 



doors were opened, only twenty-three out of the whole number re- 

 mained alive. 



From the same cause we can understand how injurious it must be 

 continually to breathe the air of ill-ventilated rooms, confined sleep- 

 ing apartments, crowded low-roofed schools, or other places in 

 which numbers are assembled together, and where ventilation is not 

 particularly attended to. A long continued and constant residence 

 in such places most certainly shortens life by several years, 

 and not unfrequently terminates it rapidly by giving rise to fatal 

 disorders. 



It must not be supposed, however, from what has been said, that 

 the carbon separated at the lungs is to be viewed as a merely 

 noxious material. If it were retained, death would undoubtedly 

 take place ; but if we had no carbon to separate we shall find that 

 the heat of our bodies could probably not be maintained. When 

 charcoal is burned in atmospheric air, the changes which occur 

 seem to be almost precisely similar to those that are produced by 

 respiration. Oxygen disappears, and carbonic acid is formed. It 

 seems reasonable, therefore, to conclude, that the heat produced in 

 both cases is connected with these changes. That the production 

 of animal heat bears some resemblance to combustion, is rendered 

 probable by the following considerations : 1st, It has been deter- 

 mined by experiment that the charcoal contained in the carbonic acid 

 formed during a given period by respiration, would give out, when 

 burned, fully more than half the heat produced by the animal in 

 that period. It takes no less than about eleven ounces of carbon 

 to form the carbonic acid of an ordinary man's daily respiration. 

 Dr. Milne Edwards thinks that this, and the superabundant oxygen 

 which is absorbed by the blood (which probably combines in great 

 part with hydrogen to form water), will account for nine-tenths 

 oi the heat an animal produces, the remaining tenth probably being 

 the product of the friction of the different parts of the body, the 

 changes occurring in secretion, &c. 2dly, This view is supported 

 by the fact, that the temperature, in the different classes of animals, 

 very accurately corresponds to the quantity of oxygen consumed. 

 The temperature of birds is highest, and they consume most. The 

 young, among the Mammalia, consume the least, and have the 

 temperature lowest. Indeed, it may be remarked, that the young 

 of most of the Mammalia, including children, have much difficulty 

 in supporting any degree of cold when separated from their 

 parents ; and where incautious exposure takes place, the mortality 





