1907.] Observations on the Life-history of Leucocytes. 497 



the first, were found in the normal mammalian spleen (figs. 4 — 8). In 

 addition, an apparently later stage was found, where the collapsed nuclear 

 membrane had almost disappeared, leaving only a few shreds (fig. 9). Hitherto 

 this phenomenon has not been observed in any other mammalian tissue than 

 normal spleen. It is probable, had the series of observations upon what 

 happened among the leucocytes of Axolotl been carried further, that the later 

 stage observed in the mammalian spleen would have been found. One 

 would also expect to find the same phenomenon taking place among the 

 leucocytes gathered together in the mammalian body under certain abnormal 

 conditions. 



There are some points of difference between the appearance of the figures 

 in Axolotl and those in mammalian spleen. The ring of chromatin masses 

 in the latter class of cells does not appear to be constant, or even frequent, 

 at that end of the tube nearest the nucleus which is destined to absorb the 

 other. Again, the evidence that the process is at first mutual, is questionable 

 in the case of mammalian leucocytes, as no undoubted cases (such as 

 shown in fig. 1) have hitherto been discovered. It may be, therefore, that 

 the process commences mutually between two cells, one eventually gaining 

 the upper hand in the case of Axolotl, while in mammals the process may 

 never be mutual at any stage ; but one cell always plays an active part, the 

 other remaining passive. No other material points of difference have yet 

 been observed. 



In both Axolotl and mammalian spleen, however, there is an immediate 

 conclusion with regard to these observations that appears quite clear. The 

 nuclear contents, at any rate the chromatin, and probably the linin, of the 

 one cell are directly absorbed by the other. The probability that the linin 

 as well as the chromatin is absorbed is very great. The chromatin masses 

 forming the rings at either end of the tube, and the strands of chromatin 

 extending from these masses, are so sharply defined that it would seem that 

 something must be holding the chromatin together in a definite form. The 

 equally sharply defined strands of chromatin that pass through the rings 

 appear to be continuous with the chromatin and linin of the nucleus. 



The process of absorption begins by the mutual throwing out of nuclear 

 protrusions of a peculiar form by two contiguous leucocytes in the case 

 of Axolotl, while in the mammalian spleen one leucocyte apparently sends 

 out a protrusion from its nucleus, which attaches itself to the nucleus of 

 another. In either case the obvious result is : (1) one cell with a nucleus 

 containing a double complement of chromatin, and probably of linin, and 

 (2) a mass of protoplasm without a nucleus, which represents what was 

 originally the other cell. 



