182 DIVISION INDUCED IN LYMPHOCYTES 



observed nicely stained and yet alive while this action 

 was taking place. At first a dilute extract was used, 

 as before, and the films in some instances were incu- 

 bated for a short time, while others were suitably 

 prepared for the room temperature. In one or two 

 cases the lymphocytes seemed to contain some rod- 

 shaped bodies in the cytoplasm. These rods stained 

 a bright scarlet, similar to the staining of chromatin, 

 and nothing had been seen like them before. They 

 certainly were not bacteria, for we have often seen 

 ingested bacteria which have quite a different ap- 

 pearance; besides, they w r ere only seen in the lympho- 

 cytes, which we have never seen to ingest bacteria. 

 With great hesitation we thought they might be 

 chromosomes. 



Before proceeding farther it is necessary to explain 

 that at the time when these experiments were made 

 the appearance presented by the chromosomes of 

 lymphocytes were unknown; in fact, it was not known 

 whether these cells from the peripheral circulation 

 divided by true mitosis or not. One of us had 

 examined leucocytes by the in-vitro method for four 

 years, and had never seen anything, previous to these 

 last experiments, w T hich appeared in any way connected 

 with division of the white blood-cells. It was appre- 

 ciated that, with the new method, a possibility existed 

 that cell-division in white blood-cells might some day 

 be seen; but to observe what appeared to be chromo- 

 somes in lymphocytes, after we had tried only one or 

 two groups of substances, seemed to be too good to be 

 realised. It was necessary to be very careful, however,, 



