180 DIVISIONS INDUCED IN LYMPHOCYTES 



trated form because more powerful solvents damaged 

 or killed the cells. In place of this nuclein, therefore, 

 extracts of some dead tissues were made, which we 

 believed would contain the dead chromatin of cells, and 

 it is said that chromatin contains nuclein. Moreover, 

 it was thought advisable to keep as closely as possible 

 to chemical substances which might be produced in the 

 body, and the insoluble nuclein which we had used had 

 been extracted by an elaborate process with hydro- 

 chloric acid. 



To obtain this extract containing as we believed 

 the chromatin of cells, we adopted a principle based on 

 our observations of the phenomenon of achromasia. It 

 may be recalled that achromasia is believed to be due 

 to the chromatin of cells passing out of them, by 

 dialysis, after their death. Achromasia will readily 

 occur if cells are allowed to die in a solution which 

 contains salt; and its onset after death is accelerated 

 by heat. We therefore made an extract of a tissue by 

 chopping it up in "citrate solution" and keeping it for 

 twenty-four hours at 60 C. The first tissue chosen 

 was lymphatic gland the reasons for this being the 

 knowledge that cancer frequently spreads through the 

 lymphatic channels and glands, that lymphocytes are 

 always seen in large numbers in growths, that lymphatic 

 glands contain large numbers of lymphocytes, and 

 especially because lymphocytes proliferate to a large 

 extent when a tissue is chronically damaged. 



The small prevertebral (haemal) glands of lambs 

 provided the lymphocytes whose chromatin we hoped 

 to extract. These glands are composed almost entirely 



