30 EXCITORS OF CELL-DIVISION 



All the agents which contain the amidine grouping 

 are effective, and we think therefore that it may 

 be said that the amidine grouping is a cause of 

 cell-division. But, in addition, there are many 

 substances which do not contain the amidine 

 grouping and yet induce mitosis. The primary 

 amines cause division provided their action is 

 augmented by choline, cadaverine, or atropine ; 

 and the same may be said of the amino-acids. 

 Yet there is a wide difference between the 

 composition of the molecules of all these groups. 

 There seems to be a large variety of substances 

 which cause the division of lymphocytes in vitro ; 

 but if the natural ones are picked out of the 

 list, it will be found that they are entirely con- 

 fined to those agents which belong to the three 

 groups amidines, primary amines, and amino- 

 acids. With regard to the two latter, we must 

 add the qualification that they are not effective 

 under the experimental conditions unless their 

 action is augmented by choline or cadaverine 

 (atropine, being artificial, may be neglected). 



This augmenting action appears only to be 

 brought about by substances which are kinetics. 

 At one time we thought that the augmentation 

 was due to the fact that the cells, being under 

 the stress of excitation (as demonstrated by the 

 exaggerated amoeboid movements), in response 

 to the kinetics, became pathologically very prolific 

 if they also absorbed an auxetic. But there are 

 several powerful kinetics, e.g. skatol, aniline, 

 trimethylamine, which are not augmentors ; a fact 

 which disproves this theory. 



Like the auxetics, there is no part of their 



