COXTEIBUTIOXS TO THE CYTOLOGY OF THE r.ACTERIA. 413 



the inakiDg of good microscopical preparations exceedingly 

 difficult and laborious, . and tliey contain granules (reserve 

 material, etc.), wliicli are relatively of such a size as to obscure 

 much of the structure of the living substance itself. For the 

 latter reasou, the sulphur Bacteria, in spite of their large size 

 in man\^ cases, appear to me to be unfavourable objects for 

 study — as a starting-point, that is to say, on our way to a 

 comprehension of the organisation of Bacteria. 



Another point that has seemed to me of some importance 

 is this. Much of the work wliich has been done upon the 

 structure of Bacteria has been based on a study of organisms 

 which have been kept in cultures for a greater oi' less period 

 of time. It seems to me highly probable that the discordant 

 results of different workei-s may in many cases be due to 

 cultural differences in the organisms studied. Different 

 culture media may be used in the cultivation of Bacteria : 

 but although " pure '' cultures may be obtained in half a 

 dozen of these, it does not follow that all or any of the 

 colonies so obtained consist of normal individuals. Bacteria 

 are not found in nature as a rule in pure cultures, and this is 

 a point which should not be overlooked when considering 

 their normal structure. Culture methods are of the greatest 

 service in the separation of various microbes from one another, 

 but it does not at all follow that all pure cultures of a given 

 organism are identical, or that they contain individuals which 

 are in ever}" way the same as those living in their natural en- 

 vironment. I have therefore not studied Bacteria grown in 

 artificial culture media, but have confined my attention for 

 the present to organisms in their natural habitat. The fact 

 that the Bacteria which I have investigated are not — for the 

 most part — previously described and named " species " from 

 pure cultures, is therefore not an objection which can be ui-ged 

 against my results, but a necessary consequence of the point 

 of view from which 1 have attacked the problem. 



As a source of material, I have found the intestinal contents 

 of various animals most useful. The contents of the large 

 intestine in many animals is swarming Avith Bacteria, frequently 



