20 EXCITORS OF CELL-DIVISION 



The substances which have the auxetic action 

 can he divided in the first instance into two main 

 groups natural and artificial. Eor convenience 

 we may use the former term as referring to sub- 

 stances which are found in the living body, or 

 which are set free in a tissue when that tissue 

 is damaged. The latter term refers to entirely 

 artificial substances not found in the body, but 

 which in most instances are manufactured syn- 

 thetically. The same terms can be employed 

 for the kinetics, although up to the present no 

 kinetic substance has been discovered which, so 

 far as we can find out, is produced physiologically 

 in the body; the natural kinetics seem only to 

 occur in pathological conditions. Up to the 

 time of writing the former publication the known 

 auxetics and kinetics were : 



AUXETICS 



Natural : extracts of dead tissues, creatine, xanthine, " globin." 1 

 Artificial : certain aniline dyes. 



KINETICS 



Natural : choline, cadaverine, neurine. 

 Artificial : certain alkaloids, especially atropine. 



In the present paper we propose to describe 

 further researches in this subject, to enumerate 

 other substances both natural and artificial which 

 have been found to be auxetics or kinetics, to 

 attempt to find out the active principle from each 

 group of them, and lastly, to discuss the bearing 

 of the knowledge gained on the problem of human 

 cell-proliferation . 



In the former publication it was shown that 



1 The filtrate of a solution of haemoglobin decomposed by heat. 



