152 BIOLOGY. [BooK n. 



Every one knows that a man obliged to live, not in complete 

 darkness, but only in a dim weak light, grows pale, languid, 

 etiolated. In this case, as we have proved above, when speaking 

 of abstinence, the nutritive exchanges are retarded. 



.To the animal, heat is much more important than light. 

 Without wishing at present to approach the study of animal 

 heat, we can already prove that animal and vegetal life is 

 only possible between certain limits of exterior temperature. 

 Doubtless animals, and especially the superior animals, do not 

 yield with a readiness as perfect as that of plants to the; 

 temperature of the exterior medium, but they only resist itl 

 up to a certain point. In all animals life is extinguished when 

 the interior temperature, that of the anatomical elements, re- 

 mains for some time below zero, for then the humours congeal. 

 In the higher mammifers death takes place even sooner. The 

 child in that state of slow asphyxia which has been called oedema 

 of the newly-born, dies when its temperature descends to about 

 20 degrees centigrade. 1 Experimentalists also indicate this 

 temperature of 20 degrees as being the minimum of inner 

 temperature. Nevertheless, the temperature of the blood may 

 descend to two or three degrees with impunity in a hibernating 

 animal, just as this animal can then sojourn without injury in 

 an irrespirable gas ; this is because the nutritive exchanges are 

 in this case extremely retarded. The anatomical elements can 

 consequently be satisfied with a small nutritive ration, which, 

 at a higher temperature, would not suffice to keep them alive. 2 



Neither is the superior limit very high. A cold-blooded 

 animal dies when a temperature 30 degrees above zero penetrates 

 its anatomical elements. For the mammifers the highest limit 

 is 45 degrees ; it rises to 50 degrees for birds. Without doubt, 

 an animal can live a certain time in these extreme temperatures, 

 but only a very short time, and on condition that the ambient 



1 Ch. Letourneau, Quelques Observations sur les Nouveau-nte, 1858. (Theses 

 de la FacuUd de Medicine de Paris. ) 



2 Cl. Bernard, Lefons sur les Proprietes des Tissus Flvants, p. 50 53. 



