TEMPERATURE AND LIFE. 425 



of the cold-blooded class at different degrees of intensity, being much 

 higher, however, than those at which warm-blooded species succumb. 

 ]n the one case they are, iu plain language, dried up, the heat depriving 

 the tissues and functions of the water necessary to their existence; in 

 the other, the vital material coagulates and life is no longer possible, 

 this cause being the more general one. This congealing, however, is 

 not always fatal, even in the case of animals of high organization. It 

 has long been known that in the northern part of America and Eussia 

 travelers transport frozen fishes, rigid and brittle, which being placed 

 in water of a temperature of 8^" and 10° regain their activity, although 

 they may have been frozen for 10 or 12 days. Science has refused to 

 believe these statements, but careful experiments have authenticated 

 them. In 1828 and 1829 Gaymard froze several toads thoroughly, and 

 they returned to their normal condition and activity on being thawed. 

 Care must be taken that both the freezing and thawing are gradual. 

 This is the principal precaution to be taken in making experiments of 

 this sort. The great English naturalist. Hunter, believed that the life 

 of man could be prolonged by being frozen from time to time. He 

 thought that if frozen and revived several times in the course of a few 

 years the limits of life could be considerably extended. Unfortunately 

 the experiment brought death instead of prolonging life. 



Let us now consider the warm-blooded organisms, the creatures whose 

 temi)erature is more stable and does not follow the thermic variations 

 iu the atmosphere about them. A mammal or a bird withstands a con- 

 siderable amount of cold. If indigenous to a cold region, protected by 

 thick fur or warm plumage, and in a position to secure the nourishment 

 it needs, it can live in a temperature at 50° below zero, its own tem- 

 perature remaining fixed and normal. It is true also of man, who by 

 protecting himself by appropriate clothing, easily withstands quite as 

 low points of temperature, particularly if there is an absence of wind. 

 We all know by experience that a moderately cold temperature with 

 wind blowing is much harder to bear than intense cold without wind. 

 The explanation of this fact is very simjde. The wind tends to con- 

 stantly deprive the body of the layer of warm air, which forms between 

 the body and the clothing, and to facilitate radiation and loss of heat 

 by substituting for it cold air. 



But what happens under experimental or natural conditions when 

 an animal or man is subjected to the action of intense cold? The organ- 

 ism withstands it for a certain length of time, but this endurance has 

 its limits, variable, it is true, according to species and conditions. A 

 moment necessarily arises, if the cold be sufficiently severe or prolonged, 

 when the organism is no longer in a state to generate sutficient heat to 

 withstand the cold or, what is practically the same, when the loss is 

 too considerable though the generation were sufficient. From that 

 moment the temperature of the animal begins to decrease. This dimi- 

 nution is compatible with life up to a certain point, which varies accord- 



