CHAPTER II 



Technique 



THE STAINING OF BACTERIA 



(8,11,53) 



THE progress ot our knowledge ot bacterial morphology has, m the 

 past, been considerably retarded by the fact, which may at first have 

 appeared advantageous, that recognisable microscopic preparations of 

 bacteria can be made by the technique of the heat-fixed film. A small quantity 

 of a bacterial culture, or of: pus, or similar pathological material, is thinly 

 spread upon a slide, dried, and then heated strongly with a naked flame, in 

 order to fix it firmly upon the slide. Bacteria fixed in this manner and stained 

 by Gram's method, or simply with a strong solution of a basic dye, dried 

 once more and examined directly under the oil-immersion lens of the micro- 

 scope (the oil serving also as a clearing agent), preserve an appearance which 

 enables them to be recognised as bacteria, and even classified within rather 

 broad limits. Their appearance under this treatment has become famihar 

 to generations ot bacteriologists, and is usually that which is recorded in the 

 descriptions o£ species. Little or no detail can be perceived in such a pre- 

 paration, and it has thus become, and until recently has remained a dogma 

 that no detail exists to be seen. This opinion is fortified by the fact that 

 equally little structure can, as a rule, be made out in unstained, hving bacteria, 

 especially as these are seldom at rest, either because of their own motility 

 or from the efirct of Brownian movement. 



It is true that, from time to time, valuable observations upon the structure 

 of bacteria have been made, either by the cytological techniques already 

 employed in other biological sciences, or by a careful study of unstained 

 material, but little attention has been paid to these findings by the great 



