CHEMICAL MESSENGERS 77 



are dependent upon some internal secretion from the ovaries 

 and testes and not upon the normal production of the male 

 and female germ-cells, or ova and spermatozoa. 



The classic demonstration of this internal messenger sys- 

 tem is that made experimentally by Berthold in fowls. In 

 1849 he transplanted the testicles of young cocks which after- 

 ward developed the masculine voice, comb, sexual desire, and 

 love of combat, thus anticipating the theories of Brown- 

 Sequard, who committed himself to the view that a gland, 

 ductless or not, sends into the circulation substances essential 

 to the normal growth and maintenance of many if not all parts 

 of the body. 



With the discovery that the regulating and balancing func- 

 tions, as well as the accelerating or retarding of the activities 

 of certain characters of organisms, are phenomena of physico- 

 chemical action, reaction, and interaction in individual devel- 

 opment, we obtain a distant glimpse of the possible causes of 

 the balance, development, or degeneration of certain parts of 

 organisms through successive generations, and conceivably of 

 the long-sought means of interaction between the actions and 

 reactions of individual development (body-protoplasm and 

 body-chromatin) and of the germ-cells in race development 

 (heredity-chromatin) . 



In fact, a heredity hypothesis was proposed by Cunning- 

 ham' in 1906 based upon Berthold's discovery that the connec- 

 tion between the germ-cells and the secondary sexual organs of 

 the body was really of a chemical rather than of a nervous 

 nature as had previously been supposed. To paraphrase Cun- 

 ningham's hypothesis in modern terms, since hormones and 

 chalones issuing as internal secretions from the groups of germ- 

 cells (ovaries and testes) determine the development of many 



^ Cunningham, J. T., 1908, pp. 372-42S. 



