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different internal secretions are more or less limited and local in their 

 effects : one affecting the activity of this and another the activity of 

 that kind of tissue or organ. Starling proposed the name hormones 

 for the internal secretions, because of their excitatory properties 

 {opjxi.u, to stir up, to excite). 



Hormones have been studied chiefly from the point of view of 

 their stimulating effect on the metabolism of various organs. From 

 the morphologist's point of view, interest chiefly attaches to the 

 possibility of their regulating and promoting the production of form. 

 It might be expected that they should be efficient agents in regulat- 

 ing form, for, if changes in structure are the result of the activities of 

 groups of cells, and the activities of cells are the results of the 

 activities of the enzymes which they contain, and if the activities of 

 the enzymes are regulated by the hormones, it follows that the last- 

 named must be the ultimate agents in the production of form. It is 

 difficult to obtain distinct evidence of this agency, but in some cases 

 at least the evidence is sufficiently clear. I will confine myself to the 

 effects of the hormones produced by the testes and ovaries. These 

 have been proved to be intimately connected with the development 

 of secondary sexual characters — such, for instance, as the character- 

 istic shape and size of the horns of the bull ; the comb, wattles, 

 spurs, plumage colour, and spurs in poultry; the swelling on the 

 index finger of the male frog; the shape and size of the abdominal 

 segments of crabs. These are essentially morphological characters, 

 the results of increased local activity of cell-growth and differentia- 

 tion. As they are attributable to the simulating effect of the 

 hormone produced by the male organ in each species, they afford at 

 least one good instance of the production of a specific change of 

 form as the result of an internal chemical stimulus. We get here a 

 hint as to the nature of the chemical mechanism which excites and 

 correlates form and function in higher organisms ; and, from what 

 has just been said, we perceive that this is the most primitive of all 

 the animal mechanisms. I submit that this is a step towards form- 

 ing a clear and concrete idea of the inner nature of the organism. 

 There is one point, and that a very important one, upon which we 

 are by no means clear. We do not know how far the hormones 

 themselves are liable to change, whether by the action of external 

 conditions or by the reciprocal action of the activities of the organs 

 to which they are related. It is at least conceivable that agencies 

 which produce chemical disturbances in the circulating fluids may 

 alter the chemical constitution of the hormones, and thus produce 

 far-reaching effects. The pathology of the thyroid gland gives some 

 ground for belief that such changes may be produced by the action 

 of external conditions. But, however this may be, the line of 

 reasoning that we have followed raises the expectation that a 

 chemical bond must exist between the functionally active organs of 

 the body and the germ-cells. For if, in the absence of a specialised 

 nervous system, the only possible regulating and coadapting mechan- 

 ism is a chemical mechanism, and if the specific activities of a cell 

 are dependent on the enzymes which it holds in combination, the 

 germ-cells of any given animal must be the depository of a stock of 



