, INTRODUCTORY. 



sublimate or a picric acid combination, washing oat with 

 alcohol, staining with alcoholic borax-carmine, imbedding in 

 chloroform-paraffin, cutting with a sliding microtome, and 

 mounting the sections in series in Canada balsam." That is 

 probably still the case, but the method can no longer claim to 

 be what it then appeared to be, the classical method of micro- 

 scopic anatomy. I suggest the following, as being quite as 

 easy to carry out, and as giving preparations far richer in 

 detail and more truthfully preserved : Fix in Flemming's 

 chromo-aceto-osmic mixture; wash out with water; dehydrate; 

 clear with oil of cedar-wood ; imbed in paraffin ; mount sec- 

 tions on the slide with Mayer's albumen medium ; stain with 

 safranin, or 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 k in- 

 vestigation. 



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. 



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, staining, treatment with successive alcohols of 

 gradually increasing strength, final dehydration with absolute 

 alcohol, clearing, and mounting in balsam. This method 

 which may be termed the dehydration method, is usually pre- 

 ferred, 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 pre- 

 servation of tissues. The presence of water is the most 

 important factor in the conditions that bring about the 



