\i\ H. GREIG SMITH. .'597 



when the investigator might easily be led astray. Certain rod- 

 shaped water-bacteria become vacuolated as they grow old; the 

 protoplasm aggregates at the poles, which stain deeply, leaving 

 the centre of the rod unstained. In these cases the central 

 unstained vacuole, and especially when it is oval, presents an 

 appearance similar to an unstained spore. When counter- 

 staining is made use of, the central vacuole does not stain. It 

 is here that perhaps the advantage of possessing a process which 

 stains the most refractory spores is evident. One can depend 

 upon the spore being stained. In the case of vacuoles, it is 

 possible, by limiting the decolorisation with acidified alcohol, and 

 by counter-staining with blue, to obtain the bacteria with their 

 dense terminal protoplasm stained red, and the vacuole pale blue. 



