414 C. CLIFFORD DOBELL. 



of large size. The consistency of the intestinal contents^ 

 moreover, is usually such as to render the makino- of micro- 

 scopic preparations (smears, etc.) comparatively easy. I 

 have found the contents of the large intestine of Amphibia 

 and Eeptilia especially suitable; but insects, mammals and 

 other animals also contain a rich supply of suitable material 

 which is as yet almost untouched. Most of the org-anisms- 

 Avhich I am about to describe have been obtained from frogs, 

 toads and lizards. 



I have found in all tlie animals which I have studied that 

 the Bacteria in the large intestine var}^ enormously — in different 

 individuals — both as regards the number of different forms, 

 and the number of microbes as a whole. In the frog, for 

 example, some individuals may contain very few Bacteria — 

 mostly of the same form — whilst others may contain countless 

 numbers of Bacteria of the most diverse forms. This is, of 

 course, only what one would expect. 



As the source of the material will be found under thfr 

 description of eacli organism, I shall here say nothing more 

 detailed ix'garding this, but will now devote a few words to a 

 description of the technique which I have employed in my 

 researclies. I have already (Dobell, 1908) given a brief 

 account of some of the methods which ] have used. 



I have tried most of the methods of fixation and staining 

 which are usually employed in cytological work. It is usually 

 necessary to modify the ordinary procedure in one way or 

 another when dealing with Bacteria. In my experience, 

 tlie usual methods of fixation (e.g. corrosive sublimate, 

 Flemming's solution, Hermann's solution, osmic acid, formalin, 

 various picric acid and bichromate solutions, etc.) may all — 

 under suitable conditions, and with careful procedure — be 

 made to give excellent results. Fixation is most easily and 

 effectively accomplished by making a wet film of the in- 

 testinal contents — or other medium in which the Bacteria 

 occur — on a coverslip, and then dropping it film-side down- 

 wards upon the fixing solution. Drying previous to fixation 

 is, of course, to be avoided. The usual l)acteriological method 



