TECHNIQUE 5 



majority o( bacteriologists, and the interpretation ot heat-fixed material has 

 not been questioned seriously. 



The main reason lor the unilorm appearance of stained bacteria is that 

 their affinity for the basic dyes which are commonly employed is so great 

 that the strongly stained cytoplasm and cell membranes mask the underlying 

 structures. This masking effect is accentuated by the shrinkage which results 

 from drying. This shrinkage is often very considerable, reducing the bacterium 

 to as little as half or a third of its natural size, and manifesting itself typically 

 in the appearance of the anthrax bacillus or of related chain-forming bacilli, 



11 



{Reproduced from the Journal of General Microbiology) 



Fig. 1. 

 THE MORPHOLOGY OF C. DIPHTHERIAE. 



A . True morphology. 



B. " Typical appearance" in heat-fixed material. The cell 

 contents are shrunken and the cell wall unstained. 



in which considerable gaps are seen between the visible bacilli, actually the 

 shrunken protoplasts. The rigid cell wall remains unstained and invisible, 

 holding the chain together. Drying and shrinkage are an essential part of 

 many staining procedures, notably those intended to demonstrate the " typical 

 morphology " o£ Corynehactcrium diphtherici\ The metachromatic granules 

 cannot be demonstrated in undried preparations, and are, in tact, artefacts 

 produced by the specific staining of a dried aggregate of nuclear and other 

 basophilic material. 



