MICHIGAN ACADEMY OF SCIENCE. 57 



of the bones of the extremities as well as by a thickening of some 

 bones e. g*., those of the skull. Other organs may also be enlarged 

 abnormally. Most of the "giants" exhibited in circuses are per- 

 sons afflicted with this hypertrophy of the pituitary body and the 

 consequent acromegal3\ The so-called secondary sexual characters 

 of the males, such as the spurs, characteristic comb and coloring 

 of the cock or the greater hairiness of parts of the body in other 

 animals or even the characteristic shape of the body, are largely 

 the result of such secretions into the blood stream from the male 

 reproductive organs. By removal of these organs in the early 

 stages of development in the individual these secondary characters 

 are almost or sometimes entirely suppressed. 



Other hormones might be cited but I believe I have made clear 

 the far-reaching specific effects of these secretions, even when in 

 small quantities. Some of these have been analyzed and have been 

 found to be of not nearly so complex a composition as enzymes or 

 proteins. They are, however, keys that fit the very complex locks, 

 the protoplasm of the various cells of the body, setting free very im- 

 portant activities. 



Now let us apply the foregoing to the chromatin masses that 

 make up the chromosomes. Why can not we assume that the 

 function of the different bits of chromatin that make up the chromo- 

 somes is to secrete substances similar to the hormones, nuclear 

 hormones we might call them, which affect the cytoplasm and 

 bring about characteristic reactions and activities in it just as the 

 hormones secreted by the thyroid glands stimulate the continu- 

 ance of the bodily and mental development, that from the pituitary 

 bodj' govern the growth of the bones, etc? Then the complete 

 complement of chromosomes or, more correctly speaking, of the 

 chromatin masses making up the chromosomes, secretes into the 

 nuclear sap a mixture of many nuclear hormones which diffuse 

 out into the cytoplasm. Here they stimulate activities and bring 

 about a development of the cell to that structure and function 

 typical for that particular organism. 



In the case of hybrids we have coming into the cells different 

 sets of chromatin masses from the different parents. In closely 

 related parents some of the chromosomes or chromatin masses 

 will be identical^ in their composition and secretions, but some 

 will be different. In some cases these different secretions may 

 not interfere with each other so that both paternal and maternal 

 characters may show on a given structure. In other cases, however, 

 one will entirely suppress the action of the other. Possibly the 



