152 BIOLOGY. [Book ii, 



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

 darkness, but only in a dim weak ligKt, grows pale, languid! 

 etiolated. In thjs 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 aiiima! 

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

 only possible between certain limits of exterior temperature 

 Doubtless animals, and! especially the superior animals, do noi 

 yield with a readiness as perfect as that ,o£ plants to the 

 temperature of the exterior medium, but they only resist i\ 

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

 the interior temperature, that of the anatomical elements, re 

 mains for some time below zero, for then the huihburs congeal 

 In the higher mammifers death takes place even sooner. Thf 

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

 of the newiy-horn, dies when its temperature descends to aboul 

 20 degrees centigrade.^ Experimentalists also indicate tHii 

 temperatiu'e of 20 degrees as being the minimum of innei 

 temperature. Nevertheless, the temperature of the blood maj 

 descend to two or three degrees with impunity in a hibernatini 

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

 an irrespirable gas ; this is because the nutritive exchanges ar( 

 in this case extremely retarded. The anatomical elements cai 

 consequently be satisfied with a small nutritive ration, which 

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



Neither is the superior limit very higli. A cold-blood6( 

 animal dies when a temperature 30 degrees above zero penetrate; 

 its anatomical elements. For the mammifers the highest limi 

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

 an animal can live a certain time in these extreme temperatures 

 but only a very short tinie, and on condition" that the ambien 



^ Ch. Letoumeau, Quelques Oiservatimis sur les Nouveau-nis, 1858. (TJiisi 

 de la FaaiMi de Medicine de Paris. ) 



^ CI. Bernard, Lemons sur les PropriStSs des Tissus Vivants, p. 50 — 53. 



