370 NUTRITION. 



apparently simple structure, into a complete organism, with 

 highly-elaborated parts. This organism has a definite form 

 and size, a definite period of existence, and produces, at a 

 certain time, generative elements, capable of perpetuating 

 its life in new beings. We may say that an organism 

 dies physiologically because the vital principle, if we ad- 

 mit the existence of a principle, has a limited term of 

 existence. But, on the other hand, the fully-developed 

 living organism, which we call an animal, presents numerous 

 distinct parts, each endowed with an independent property 

 called vital, that property recognized by Haller in various 

 tissues, under the name of irritability ; and it is the coor- 

 dinated sum of these vitalities that constitutes the perfect 

 being. These are more or less distinct ; and we do not com- 

 monly observe a sudden and simultaneous arrest of the vital 

 properties in all the tissues, in what we call death. For 

 example, the nerves may die before the muscles, or the mus- 

 cles, before the nerves. It is also found that vital properties, 

 apparently lost or destroyed, may be made to return ; as in 

 resuscitation after asphyxia, or the restoration of muscular or 

 nervous irritability by injection of blood. 



The life of a fecundated ovum is the property which 

 enables it to undergo a certain development when placed 

 under favorable conditions ; and, by the surrounding condi- 

 tions, its development may be arrested, suspended, or modi- 

 fied. The life of a non-fecundated ovum is like that of any 

 ordinary anatomical element. 



The life of an anatomical element or tissue in process of 

 development is the property by virtue of which it arrives at its 

 perfection of organization, and performs certain defined func- 

 tions, as far as its organization will permit. This can also be 

 destroyed, suspended, or modified by surrounding conditions. 



The life of a perfect anatomical element or tissue is the 

 property which enables it to regenerate itself and perform its 

 functions, subject, also, to modifications from surrounding 

 conditions. 



