CHAPTER IV. 



OF THE GENERAL CONDITIONS OP GROWTH. 



Growth is essentially the result of the predominance of assimi- 

 lation over disassimilation, that is to say, it -cannot be effected 

 without the concurrence, the immediate presence of a sufficient 

 provision of assimilable materials. But the living anatomical 

 elements seem sometimes capable of profoundly modifying and 

 metamorphosing these materials in a great degree. According 

 to M. CI. Bernard, the larvae of flies form their organised 

 tissues from substances soluble in alcohol, and consequently 

 deprived of albuminoidal substances, properly so called. Not- 

 withstanding, as a general rule, a certain analogy of chemical 

 construction is necessary between the different kinds of histo- 

 logical elements and the blastemas, at the expense of which 

 these elements live and develop themselves. If, for example, 

 we transplant, by animal grafting, the anatomical elements of 

 one animal to another, the operation will be likely to succeed 

 in proportion as the animal species are analogous. 



As to the general conditions of heat, light, oxygenation, and 

 alimentation, we must refer to the chapters treating of nutrition, 

 and limit ourselves to pointing out the particular facts relating 

 directly to growth itself. 



It has been pretended that certain animals, certain tissues, can 

 live and develop themselves without oxygen. These paradoxical 

 facts must only be received with extreme reserve. They have, 

 without doubt, been insufficiently observed, badly elucidated, and 

 are included probably in the general law, according to wliich 



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