74 THE ORIGIN AND EVOLUTION OF LIFE 



ferent manner from the antitoxins. While antibodies of this 

 kind tend to assimilate or remove the invading antigen, they 

 do not confer immunity against a future invasion: on the con- 

 trary, they render the organism increasingly susceptible. Ex- 

 periments on animals show that, while the first injection of 

 such inactive proteins may be entirely harmless, subsequent 

 injections may result in severe injury or even death. 



It is, therefore, evident that the invasion of an organism 

 either by a powerfully active or by an inactive antigen causes 

 changes of a physicochemical nature which appear to originate 

 in the body cell itself, resulting in the formation of chemical 

 messengers known as antibodies which appear in the circulat- 

 ing blood. 



Fourth: Of vital importance to the life organism are those 

 chemical messengers known as internal secretions, due for the 

 most part to the so-called endocrine (Gr. evhov, within, and 

 Kpivoi, to separate) organs or ductless glands, which liberate 

 some specific substance within their cells that passes directly 

 into the blood stream and has a stimulating or inhibiting effect 

 upon other organs. To certain of these stimulating internal 

 messengers Starling applied the term ''hormone" (Gr. op/xdo), 

 to awaken, to stir up). Recently Schafer,^ in reviewing all 

 the organs of internal secretion, has proposed the opposite 

 term "chalone" (Gr. x"^'^'^, to make slack) for those messen- 

 gers which depress, retard, or inhibit the activity of distant 

 parts of the body. The interactions between different parts 

 of the organism produced by these chemical messengers depend 

 upon a simpler chemical constitution than that of the enzymes,- 

 as hormones and chalones, for the most part, are not rendered 

 inactive, even by prolonged boiling. 



We may suppose that in the course of evolution certain 



' Schafcr, Sir Edward A., 1916, p. 5. - Loc. cit. 



