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SCIENCE 



[N. S. Vol. XXXII. No. 830 



system, and as we ascend the scale of organ- 

 ization, this assumes a greater and greater 

 importance as a coordinating bond between 

 the various organs and tissues of the body. 

 But the more primitive chemical bond per- 

 sists, and is scarcely diminished in im- 

 portance, but only overshadowed by the 

 more easily recognizable reactions due to 

 the working of the nervous system. In 

 higher animals we may recognize special 

 chemical means whereby chemical co- 

 adaptations are established and maintained 

 at a normal level, or under certain circum- 

 stances altered. These are the internal 

 secretions produced by sundry organs, 

 whether by typical secretory glands (in 

 which ease the internal secretion is some- 

 thing additional and different from the 

 external secretion), or by the so-called 

 ductless glands, such as the thyroid, the 

 thymus, the adrenal bodies, or by organs 

 which can not strictly be called glands — 

 namely, the ovaries and testes. All these 

 produce chemical substances which, pass- 

 ing into the blood or lymph, are distri- 

 buted through the system, and have the 

 peculiar property of regulating or exciting 

 the specific functions of other organs. Not, 

 however, of all the organs, for the differ- 

 ent internal secretions are more or less 

 limited and local in their effects: one af- 

 fecting 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 ex- 

 citatory properties (op/xcfo), to stir up, to 

 excite) . 



Hormones have been studied chiefly 

 from the point of view of their stimiilating 

 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 regu- 



lating 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 activi- 

 ties 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 ob- 

 tain distinct evidence of this agency, but 

 in some eases at least the evidence is suffi- 

 ciently 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 devel- 

 opment of secondary sexual characters — 

 such, for instance, as the characteristic 

 shape and size of the horns of the bull ; the 

 comb, wattles, spurs, plumage color 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 differentiation. As they 

 are attributable to the stimulating 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 mech- 

 anism 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 forming a clear and con- 

 crete idea of the inner nature of the organ- 

 ism. 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 condi- 

 tions or by the reciprocal action of the ae- 



