No. 2.] CHANGES IN NERVE CELLS. 99 



There is, indeed, little enough consensus. In no field of biology- 

 is there such a Babel of discord, and the reason for this is 

 obvious. The material of observation here is not permanent 

 form, but flitting, vanishing, ever-changing phases of action. 

 What one observer sees is gone before another observer can 

 confirm it. Further than this, and aside from the difficulty of 

 making exact observations, the causes which modify or influ- 

 ence cellular activity are little understood. Hence causes which 

 might account for difference in results are likely to be over- 

 looked, and results themselves are claimed to be different ; con- 

 siderations like the above will be of assistance as we proceed. 



What Minot (52, p. 98) would say of the whole organism is 

 true of its individual cells. No process is more characteristic 

 of living protoplasm than growth. And growth in a metazoan 

 may be due to either cell-multiplication or to cell-growth. The 

 first is plainly reproduction. May not also cell-growth (57, p. 23 ; 

 51, p. 439) be considered in essential nature, a process of the 

 same kind, in which the increment of matter gained is used 

 for some other purpose by the cell than that of reproducing 

 another cell like itself .? An amoeba, or a tissue-cell, grows and 

 then divides into two cells, we will say, of exactly the same 

 kind, and half the size of the original. A working tissue-cell 

 grows to twice normal size, but, instead of dividing, it now 

 throws off half of its substance, let us say, in the form of zymo- 

 gen granules. That is to say, the cell has become specialized, 

 so that instead of dividing into two equivalent parts it divides 

 into two unequal parts ; the one remaining as the original cell, 

 the other passing off to do the work for which the cell has 

 become specialized to perform. If there is any truth in this 

 view, we should expect to find the same mechanisms which 

 mediate cell-reproduction active in cell-function. Exactly what 

 the reproductive mechanisms of a cell are, despite the^ vast 

 amount of work devoted to the subject, is still a matter of con- 

 troversy. I shall attempt no special discussion, and hence shall 

 refer to but two or three papers which bring out points of imme- 

 diate use to us, bearing upon the general subject of cellular 

 activity. 



In the process of division no part of the cell is likely to show 

 such active changes as the nucleus. In fact, the nucleus is not 

 infrequently called the reproductive organ of the cell. May not 



