106 PHYSIOLOGY. 



5. Living animal bodies have not only the faculty of pro- 

 ducing heat, but they can also resist heat of a much higher 

 temperature than their own bodies. The heat of the body 

 is kept at its usual standard of 98 degreesjby the exhalent 

 vessels of the skin, which absorb by means of the perspira- 

 tion tho excess of caloric, and fly off with it in a state of 

 vapour^ 



6. In very hot weather, those functions of the body, such 

 as digestion, nutrition, and secretion, on which tho produc- 

 tion of animal heat depends, are weakened by the excessive 

 heat, so that in fact less caloric is produced in the system 

 than in cold wcathcrX This is a wise provision of Providence, 

 that when much internal heat is wanted to guard against the 

 cold, it is produced ; when less is needed, on account of the 

 warmth, the system generates less. 



7. Animal bodies are also capable of developing electricity ; 

 as most of the bodies which surround us are conductors of 

 the electric fluid, it generally passes off as fast as it is 

 formed. Sparks of fire, however, are often seen in winter, 

 on taking off in the dark, silk dresses or stockings, or flannel 

 drawers. Some physiologists maintain that the nervous 

 power is nothing but the electric fluid ; but though this may 

 not be admitted, there is a very close analogy between them. 



8. It has also been found that needles plunged into the mid- 

 dle of a nerve, become magnetic, and are capable of att r;i i- 1 i n ; 

 light substances, such as pieces of paper ; and a physiologist 

 by the name of Weinhold says, that he has seen sparks 

 obtained by bringing tho divided ends of a nerve together. 

 Muller mentions in his late work on Physiology, that cffi- 

 cient galvanic piles can be constructed from organic sub- 

 stances, without any concurrence of metals. Concentrated 

 solutions of organic substances were spread upon thin paper, 

 and with disks of this, paper piles constructed, the t\\o l;nvrs 

 of different substances being separated by two thicknesses of 

 paper ; electricity was developed by these piles, and tested 

 by an electrometer. It would seem from these experiments, 



