TRANSPLANTATION AND INDIVIDUALITY. l6l 



CONTACT SUBSTANCES AND HORMONES; THEIR RELATION TO THE 

 INDIVIDUALITY DIFFERENTIAL. 



These contact substances are contrasted with the hormones, 

 for instance those given off by the corpus luteum which regulates 

 the activity of the mucosa of the uterus and probably of certain 

 other organs. They are given off by certain organs, and carried 

 through the circulation to distant organs. They have a specific 

 distant action. In contradistinction to some of the contact sub- 

 stances these distance substances do not possess an individuality 

 or even a species differential. 



CONTACT SUBSTANCES AND CHANGES IN OLD AGE. 



I cannot conclude a consideration of this aspect of the subject 

 without pointing out the similarity of conditions which we find 

 under " homoio conditions " with those found in old age. In both 

 cases we observe a tendency to the formation of a fibrous stroma 

 and to a decrease in good vascularization. This condition also 

 corresponds to that found in states of metabolic inactivity. May 

 we not therefore refer old age changes not only to the lack of 

 certain hormones given off by glands (as for instance thyroid and 

 corpus luteum) with internal secretions, but also to a quantita- 

 tive or sometimes perhaps even to a qualitative change in the 

 character of contact substances, to a diminution in the produc- 

 tion of what we have called the " auto substances " ? Such a 

 diminution in auto substances would be the necessary result of a 

 diminished activity of the parenchyma. Thus a vicious circle 

 would be established. The diminished activity of the paren- 

 chyma causes changes in stroma and vascularization and the latter 

 further depresses the activity of the parenchyma. 



INHERITANCE OF THE INDIVIDUALITY DIFFERENTIAL. 

 We have seen that there is in each individual and in each cell, 

 at least in the large majority of all cells of an indivdual, an indi- 

 viduality differential which is present in addition to the ordinary 

 Mendelian unit factors. The inheritance of the latter has given 

 rise to numerous investigations which on the whole have tended 

 to show the general applicability of Mendelian rules in the in- 



