tempp:ratuke and life. 417 



reaction it probably exercises upon the other thermogenic chemical 

 actions. As to waste, this is incurred in accordance with well-known 

 physical laws, and with warm-blooded animals it is sometimes facilitated 

 and sometimes diminished by the action of the regulating mechanism 

 placed under the dependence of the nervous system, a mechanism 

 which in its normal condition tends to preserve for the organism a tem- 

 perature nearly constant, diminishing the losses when the production 

 of heat is feeble or insufficient in respect to the temperature of the sur- 

 rounding medium, and augmenting these losses, on the contrary, when 

 the atmosphere is too higli, or when the production is so great that it 

 tends to intiame the bodily organism. 



The only difference, from the physiological standpoint, in the calori- 

 fication which exists among warm blooded and cold-blooded animals 

 is, that with the latter the production of heat is slight and the regu- 

 lating apparatus absent. These species engender little heat, and are. 

 unable to regulate their losses. They also follow the variations in the 

 outside temperature almost to as great an extent as inanimate objects; 

 whereas warm-blooded animals conform in a less degree to the outer 

 atmosphere, and also with less impunity. 



II. 



We are now to consider between what limits of temperature organic 

 life can be maintained. Animals of the highest temperature, protected 

 though they are against the extremes of heat and cold, can be placed 

 under conditions which render these protective means inadequate, and 

 this in a state of nature and apart from all experimentation. 



A word first on the thermic variations which occur in the inhabited 

 zone of our planet ; a zone limited in extent, comprising an average of 

 8 to 10 kilometres in altitude, its elevations and depressions being 

 about equal in distance from the level of the sea; a zone exceedingly 

 small when compared with the diameter of the earth. Beyond the 

 limits of this region life has never existed, or at least exists no longer. 

 We are more especially interested in that portion of the earth which 

 can support organic life. The extreme points of temperature observed 

 in the atmosi)here are 70° and + 5(P C. The former observation was 

 made at lakoutsk, the latter at Mourzouk. These arc vsaid to represent 

 very exactly the extreme limits, forming a difference of 125° or 130°C. 

 At these far distant points human life is possible, and also that of cer- 

 tain animals. In the ocean tlie thermometric digressions are not as 

 great. According to Wyville Thompson, the temperature of the At- 

 lantic Ocean reaches 0° at a depth of only 4,200 metres; at 0,000 metres 

 it registers 5°; at 800 metres, 4°, and at 2,000 meties it is 3°. About 

 the same can be said of the Pacific Ocean. Should the temperature 

 upon the surface or at the bottom of the sea descend lower than — 1° 

 or — 2° the water freezes. It is not necessary for us to consider this 

 H. :\[is. 129 27 



