266 president's address. — section d. 



It seems certain that in all forms of mnemic theory we shall in 

 future find the recognition, already noticeable, of the part played by 

 chemical substances, especially of hormones, or of substances that in 

 given circumstances act as hormones. 



That chemical compounds may be formed in a definite and charac- 

 teristic sequence in an organism has been amply demonstrated. In 

 such a sequence each compound is the signal, even the efiective stimulus, 

 for the production of its successor. That even a single cell may at one 

 moment produce one substance and at the next a different substance 

 in a definite order cannot be doubted. Loeb (loc. cit., p. 253) observed 

 that in experiments on artificial parthenogenesis, the action that brought 

 about the formation of the fertilization membrane was a cytolytic 

 action. If this was not checked complete cytolysis of the egg took 

 place. If, however, immediately the membrane had been formed, 

 the egg was removed to a hypertonic solution, cytolysis was checked 

 and, in successful cases, fertilization was effected. The light that this 

 throws on natural processes leads Loeb to observe, " Since the entrance 

 of the spermatozoon causes that degree of cytolysis which leads to 

 membrane formation, it is probable that in addition to the cytolytic 

 or membrane-forming substance (presumably a higher fatty acid), 

 it carries another substance into the egg, which counteracts the dele- 

 terious cytolytic effects underlying membrane formation." 



The knowledge that we begin to have of hormones and of enzymes 

 makes it not impossible to conceive of development as comprising a 

 series of ontogenetic stages each determined by the preceding stage '^ 

 at each stage, what has been called cell memory brings about the 

 appearance of the chemical substance that will provoke advance to the 

 next stage, Tliis persistence of an ancestral stimulus is comparable 

 to the persistence of st'muli in the central nervous system to result 

 time and again in the phenomenon that we call memory. 



