142 SCIENCE PROGRESS. 



in general, and I think I may safely say that no one who 

 has had much experience in actually watching the effect of 

 reagents on the living cell will be inclined to under-estimate 

 its importance. 



I am not now speaking of those obvious contractions and 

 distortions, the well-known results of defective treatment of 

 the material at some stage between killing the protoplasm 

 and finally observing its structure with the aid of the micro- 

 scope. I am thinking rather of the insidious effects of 

 certain reagents which, in some cells and tissues at any rate, 

 are able to evoke post-nwrteni changes so definite in their 

 character that only careful and wide comparison enables 

 one to set them down as undoubtedly artificial. It may be 

 the reagent was too much, or too little, concentrated, or that 

 it happened to be unsuitable for some reason or another to 

 the particular tissues under investigation. 



But there are other perils, of a more general, and per- 

 haps one may say of a more subjective, nature, to which 

 the student of cytology is specially liable. I refer in par- 

 ticular to that one of over-generalisation. The fact is, the 

 subject is so essentially a study of an enormous number of 

 minute details, the relative importance of which is still for 

 the most part uncertain, that one is more than usually exposed 

 to the danger of drawing too wide conclusions from too 

 narrow an area of fact. That this is a real and not a 

 fanciful charge, a slight acquaintance with the first-hand 

 literature of the subject is enough to prove ; elaborate 

 general theories are based on the study of, it may be, a 

 particular set of nuclei belonging to a single organism. The 

 time so spent would have been better employed in extend- 

 ing the authors' range of vision over other groups of the 

 animal and vegetable kino^dom. 



The phenomena which are successively exhibited during 

 the processes resulting in the formation of the reproductive 

 cells in Ascaris megalocephala, for example, and in their 

 fusion during the act of fertilisation, are so striking that it 

 is small wonder that they have been, and by some people 

 -seem still to be, regarded as representing a general type to 

 which other organisms ought to conform, at least in the 



