CHAPTER IV 



THE NATURE, MODE OF ACTION, AND ORIGIN OF HORMONES 



HORMONES may conceivably be of two kinds namely, 

 augmentary and inhibitory analogous in their action to the 

 two well-known kinds of nerve fibres. But it would seem 

 probable that the inhibitory is in many cases the only active 

 influence exerted. This may be regarded as a putting on of 

 the brake, while the augmentary influence is simply a case of 

 removing the brake. In other words, the organs have a 

 superabundance of stored energy, and are constantly tending 

 to over-activity. The normal degree of activity is determined 

 by inhibitory influences. These influences may be nervous, or, 

 as we have seen, they may be chemical. 



But there seem to be some definite examples of augmentary 

 hormones, as, for example, secretin and adrenin. The two 

 groups are sometimes called " assimilation " and " dissimila- 

 tion " hormones. 



Sir E. Sharpey Schafer suggests the name " autocoid sub- 

 stance " instead of " hormone," and restricts the term " hor- 

 mones " to the excitatory autocoid substances, while those 

 whose actions are inhibitory are called " chalones." Matthews 

 has recently introduced the term " cryptorhetic tissues " as 

 applied to those furnishing an internal secretion. These organs 

 and tissues are also often referred to as " endocrine " or 

 " endocrinous," and the subject as " endocrinology." 



Nothing definite can be stated about the origin of hormones 

 in general. In the case of some of the individual hormones, 

 the matter may be discussed in its proper place. 



The hormones which have so far been described are secretin, 

 the gastric hormone, the hormones of the liver, pancreas, 

 kidney, testis, ovary, and corpus luteum, as well as adrenin 

 and the active substances of the thyroid apparatus and the 

 pituitary body. 



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