34 



proves the identity of that stimulus with the one which forms so im- 

 portant a part of the animal economy; an observation further illus- 

 trated by the fact that a purely mechanical stimulus, such as the ap- 

 plication of a needle, will excite muscular action after life has ceased. 

 If moreover temperature, arterialization, digestion, &c, were all pro- 

 duced by electric agency, this would surely be manifested by delicate 

 instruments j but no such manifestation is obtained. Still further, it 

 is worthy of observation that in those animals (such as the Gymnotus 

 electricus and the Torpedos) which are endowed with electric power, 

 a peculiar apparatus exists for the development of such power. On 

 the whole, indeed, it appears that modern physiologists have scarcely 

 advanced in the explanation of the causes of animal temperature be- 

 yond that given by John Hunter, who says, " It is most probable that 

 it arises from some other principle; a principle so connected with life, 

 that it can, and does, act independently of sensation, circulation, and 

 volition ; and is that power which preserves and regulates the internal 

 machine. This power of generating heat is in the highest perfection 

 when the body is in health ;" and the energy of the vital principle is, 

 in fact, the scale by which we can estimate the power of the body 

 to sustain its temperature. 



There are many circumstances which modify the effects of tempe- 

 rature upon animals and render them more susceptible of a low tem- 

 perature. Such are want of exercise, inappropriate food, impure at- 

 mosphere, exhaustion whether from fatigue or hunger, immature age, 

 season, and the quality of the air as to humidity or dryness. These 

 were severally considered. 



The excitement produced by exercise, the activity imparted by it 

 to the circulation, and the glow which it gives to the system, all tend 

 to render an animal less susceptible to the effect of a low tempera- 

 ture. Dens therefore in which animals are kept should be of sufficient 

 size to allow of the taking of free exercise. Its importance is strongly 

 illustrated by the fact that in very cold or elevated situations cessation 

 of motion is destruction, well known instances of which are the cases 

 of Sir Joseph Banks and Dr. Solander, and of Dr. Richardson. 



The quality of the food is of the greatest importance, and should 

 be regulated as nearly as possible in accordance with the habits of 

 the animals in a state of nature. This subject requires therefore ex- 

 tensive inquiry and observation. There is, however, one part of it 

 which is deserving of particular notice as connected with climate. 

 In the quality of his nourishment man is guided by the climate in 

 which he lives. The Esquimaux adopts a food entirely animal. The 

 Hindoo uses a diet solely vegetable, employing condiments only to 

 counteract the flatulency which such food is likely to produce. The 

 inhabitants of northern countries take, and without material injury, 

 stimulating liquors ; — the use of such beverages is borne very badly 

 by the natives of India. In cold and elevated regions stimulating 

 diet appears therefore to be indicated, and it seems consequently ad- 

 visable to furnish such, including even spirits or fermented liquors, to 

 tropical animals kept in our climate during the cold season. 



Air vitiated by respiration is deprived of the requisite stimulus to 



