CHAPTER III 

 METABOLIC GRADIENTS IN ORGANISMS 



If metabolic gradients are of such fundamental impor- 

 tance in the organic individual it should be possible to 

 discover various proofs or indications of their existence. 

 This chapter is a survey of some of the experimental 

 and observational evidence for the existence of metabolic 

 gradients. 



SUSCEPTIBILITY GRADIENTS IN ANIMALS AND PLANTS 



The resistance or susceptibility of living protoplasm 

 to various poisons can be used, with certain precautions 

 and within certain limits, as an index of its metabolic 

 condition. This method, which may be called the sus- 

 ceptibility method, makes it possible, particularly in 

 early stages of development and in small, simple animals, 

 to compare the susceptibilities and so to obtain a general 

 idea of the differences in metabolic activity of differ- 

 ent regions of the body of a single organism. Many 

 different substances may be used as reagents for deter- 

 mining susceptibility, such, for example, as the alcohols, 

 ethers, and other narcotics, and acids and alkalies. 

 Various products of metabolism, among them carbon 

 dioxide, and certain conditions, such as lack of oxygen, 

 serve the same purpose. But the cyanides, which are 

 powerful poisons, are in many respects the most satis- 

 factory reagents, and they have been used in most of 

 my experiments. 



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