270 THE DIVISION OF LEUCOCYTES 



amount of the agent absorbed. The division of 

 the centrosome seems to be part of this cycle, but 

 how long this part takes we do not know. Hence it 

 appears possible that what is commonly known as 

 the resting stage is in reality the time occupied by 

 the division of the centrosome. 



The method of division of leucocytes and lympho- 

 cytes is so constant that we thought it was reasonable 

 to expect that the proliferation of healing would be 

 ultimately proved to take place by a similar process, 

 and that if so there must be produced in an injured 

 tissue some chemical substance very similar in its effects 

 to that contained in azur dye. Up to this time, however, 

 we had not succeeded in inducing divisions at all with 

 any substance which we could call a "natural" sub- 

 stance. There is nothing in the body that we know of 

 at all like the aniline dye. It was true that an extract 

 of dead haemal gland augmented the action of the ani- 

 line dye; but it would not induce divisions by itself. 

 Extracts of tissues other than haemal gland were tried, 

 made in the same strength namely, 100 per cent and 

 it was found that suprarenal glands of sheep augmented 

 the action of the stain in inducing divisions even better 

 than haemal gland, and several extracts, such as those of 

 muscle and liver, did the same, but to a lesser degree. 

 In spite of the augmenting action of all these extracts, 

 however, none of them alone in the strength tried would 

 induce divisions either in lymphocytes or leucocytes in 

 the experimental ten minutes. 



This inability to cause cell-division by entirely 

 "natural" substances, such as the extracts named, was 



