INTRODUCTORY. 5 



double-stain with gentian-violet and eosin; and mount in 

 balsam or damar. That, or something like that, is now the 

 practice of many of the most advanced workers ; and I know 

 of no method that seems to have equal claims to be considered 

 a classical method of general morphological investigation. 



As regards the method to be used for imbedding, I take it that the paraffin 

 method is the method par excellence for small objects (objects up to 5 or 7 

 millimetres diameter) ; whilst the collodion or " celloidin " method is the 

 method par excellence for large objects. 



As regards the rival claims of the method of staining objects in toto before 

 section cutting, and that of staining the sections, I confess that I cannot see 

 any reason for preferring the practice of staining in toto, which I consider 

 only has a raison d'etre in the case of objects which are not to be cut into 

 sections. 



As regards the rival claims of the practice of staining sections on the slide, 

 and that of staining them in watch-glasses, I think that all small sections 

 may be conveniently stained on the slide, and that all large ones should be 

 stained in watch-glasses ; in other words, the watch-glass process is the proper 

 process for celloidin sections, and the slide process is the most convenient one 

 for paraffin sections. 



3. The treatment of objects which can be studied without 

 being cut into sections is identical with that above described, 

 with the omission of those passages that relate to imbedding 

 processes. Its normal course may be described as fixation, 

 washing out with alcohol, staining with alcoholic borax-carmine 

 or some other alcoholic stain, treatment with successive alco- 

 hols of gradually increasing strength, final dehydration with 

 absolute alcohol, clearing, and mounting in balsam. This 

 method, which may be termed the dehydration method, is 

 generally preferred, as a general method, to what may be 

 termed the wet methods, by which objects are prepared and 

 preserved in aqueous media. The chief reason for this lies in 

 the great superiority of the dehydration methods as regards 

 the preservation of tissues. The presence of water is the 

 most important factor in the conditions that bring about the 

 decomposition of organic matter, and its complete removal is 

 the chief condition of permanent preservation. 



It is of course not intended here to suggest that wet methods of prepara- 

 tion should be altogether discarded. They have great value, they are even 

 indispensable, for special ends ; and all that is intended to be suggested is, 

 that they should be regarded not as general but as Special methods. 



4. In the preparation of entire objects or structures that 



