REPORT ON ANIMAL PHYSIOLOGY. 109 



that they are the immediate effects of the mechanical oi* chemical 

 impressions, but assert that they are the ejRFects of powers which 

 the external impression, be it mechanical or be it chemical, has 

 thus solicited to act." 



Of these excitants some are necessary conditions of life, 

 and are therefore called vital stimuli. Plants cannot live any 

 considerable time without air, water, warmth, and light ; nor 

 animals without the first three, and they become rickety when 

 deprived of the last. These being indispensable for the due 

 nutrition of parts, are necessary for the sustentation of those 

 powers which are developed with the parts by the act of nutri- 

 tion. But all animals are not dependent upon each of these 

 excitants in an equal degree. Thus, the new-born of warm- 

 blooded animals resist more easily the deprivation of air than of 

 warmth. They are drowned more readily in cold water than in 

 warm, within certain limits of warmth. They live longest 

 under water between 20 — 30° R., and if the heat be above or 

 below these limits die sooner. In general, the lower the place 

 of the animal in the zoological scale, the longer can it bear to 

 be deprived of these stimuli. Amphibia live from ten to thirty 

 hours, in distilled water, under the air-pump ; and frogs, whose 

 lungs have been extirpated, may survive thirty hours. 



With respect to the stimulus of food the same general rule 

 prevails ; the intervals of supply may be greater without destroy- 

 ing life in animals, according as their organization is less com- 

 plicated, and their powers more limited. Thus, tortoises and 

 sei'pents may be deprived of food for months, and many mollusca 

 for yet longer periods. 



Some also of the internal conditions of life may, in the lower 

 animals and in the imperfect states of the higher, be suppressed 

 or greatly altered, and yet life be supported for a longer or a 

 shorter period. The experiments of Legallois and others lead 

 to the conclusion, that this period varies inversely as the per- 

 fection of the organ whose action is suppressed. The Batrachia 

 are found to live for many hours without the heart ; a tortoise, 

 whose brain was i-emoved by Redi, lived after the operation for 

 several months ; in new-born rabbits, if the heart be extirpated, 

 sensibility persists for about fourteen minutes ; when they are 

 fifteen days old, for only two and a half minutes ; thirty days old, 

 one minute* ; and the young of man may, at the time of birth, 

 be revived when the heart's action has ceased for a period after 

 which, in the more adult state, it could not be restored. 



In the more perfect forms of life there is a necessary depend- 

 ence of the whole organism upon each of its parts, and of the 



* Essai, Legallois, p. 142. 



