72 FEEDING ANIMALS. 



oxygen and throws off carbonic acid, and when this action 

 is interrupted the health of the' animal suffers. The true 

 skin underlies the scarf skin, and is filled by capillary 

 blood-vessels, and it is in its passage through these capil- 

 laries that the blood gives off carbonic acid and absorbs 

 oxygen. The amounts thus given off and taken up are 

 quite considerable. The excretions from the skin in the 

 form of "insensible perspiration," also carries off large 

 amounts of water. 



This also is the means of relieving the body of surplus 

 heat. Millions of pores permeate the skin, and large vol- 

 umes of vapor are given off through these pores. These 

 orifices are exceedingly minute, convoluted tubes, lying 

 under the skin, and are found to be from one-fifteenth to 

 one-tenth of an inch in length. Erasmus Wilson estimated 

 the number of these tubes in every square inch of the sur- 

 face of the body to be 2,800, and the total number of square 

 inches on the surface of the body of an average sized man 

 to be 2,500, therefore his skin is drained with 28 miles of 

 these tubes, having seven millions of openings. "Water, 

 when converted into vapor by the heat of the body, ex- 

 pands to 1,700 times its liquid bulk, and in doing this ab- 

 sorbs a large amount of heat, and the watery vapor escapes 

 through the pores of the skin, thus cooling the body. 



This shows the immense importance of regulating the 

 temperature of the atmosphere surrounding the bodies of 

 animals, as all the heat of the body, as well as its growth, 

 comes from the food. 



ANIMAL HEAT. It was formerly supposed by physiolo- 

 gists that animal heat was produced by the oxidation or 

 combustion of the carbon of the food in the lungs, by 

 means of the oxygen inhaled. But later investigations 

 explain these phenomena in a different manner. Dr. 

 Armsby, in his late work, explains this later theory con- 

 cisely, thus : 



