TEMPERATURE AND LIFE. 411 



eiable difference in their temperature. This is iu spite of the fact that 

 in living organisms the equal distribution of temperature is favored by 

 the con tact of heated portions with those which are less so, either directly 

 or indirectly, by the circulation of the blood. In spite of this tendency 

 to establish an equality of temperature, it is easy to distinguish those 

 of the highest temperature. They are naturally those of most activity^ 

 from a chemical standpoint, and whose respirations are most frequent* 

 The liver, brain, glands, heart, and muscles belong to this class. The 

 heat generated by tiiese organs is in proportion to the chemi(!al activity 

 and to the amount of work which they themselves perform. Every 

 organ is, in fact, warmer when in a state of activity than when in a state 

 of repose. 



Caloriflcatiou is thus the result of chemical phenomena which take 

 place in the recesses of the tissues. These phenomenn, which are nu- 

 nierous and active iu animals of the higher class (homeotherms), are 

 much less so in cold-blooded animals; but this point is not important,, 

 the difference being in degree, not in kind. 



Here a question arises : Why does man have an equable temperature 

 at the poles, where the temperature is 30 degrees below zero, and iu 

 Sahara, where there are 40 degrees of heat I Why are not man and 

 warm-blooded animals influenced to a greater degree by the temperature 

 ill which they live, and how are they enabled to contend with these ex- 

 tremes of temperature? In several ways, from a physiological stand- 

 point, for at this time we are not to consider the means devised by man 

 for his protection. To enable him to endure extreme heat, he is supplied 

 with a sudatory apparatus which acts as soon as the internal tempera- 

 ture begins to rise. The action of external heat brings the sudatory 

 glands into activity, and evaporation of the perspiration produces re- 

 frigeration to a marked degree. Note, by the way, that this evapora- 

 tion is only possible in an atmosphere relatively dry, and is less in pro- 

 l)ortion to the humidity of the atmosphere surrounding the body. On 

 tliis account one suffers more from heat when the air is full of moisture 

 than when it is dry. Ilumidity impedes and retards evaporation, and 

 in consequence also refrigeration. 



Certain animals are endowed with this sudatory apparatus for the 

 same purpose as man, but many of them are entirely without it. Among 

 the latter class are birds, dogs, rabbits, etc. In what way are these 

 protected against heat? As far as we know, no researches have been 

 made on this i)oint in regard to birds ; but concerning dogs, M. Ch. 

 Kichet has reached very interesting conclusions. In this animal refrig- 

 eration is effected by means of the respiratory organs, for it is bj^ this 

 means only that they can bring about a copious evaj)oration. The dog 

 perspires through his lungs, as is the case with all creatures which 

 have this organ, even man himself, but with the dog this is the only 

 means of effecting perspiration, and it is therefore eini)loyed to a far 

 greater extent. When a dog is heated he thrusts out his tongue in 



