STAINING BACTERIA. 189 



" The strength of the acetic acid solution is not of 

 much consequence. The best solution is one contain- 

 ing only a small percentage of the acid, and it is well 

 not to allow it to act too long. The other manipula- 

 tions, such as the removal of water, clearing up, and 

 mounting, are exactly the same as in the preparation 

 of other microscopic specimens. One must avoid leav- 

 ing the sections too long in alcohol or oil of cloves; 

 otherwise the staining material will be washed out by 

 these fluids." l 



The method above described brings to view the 

 larger forms of bacteria which may be distributed 

 through the tissues ; but, according to Koch, the 

 smaller forms may not be distinguished, although 

 deeply stained, and require for their demonstra- 

 tion a special form of illuminating apparatus, 

 which brings out the " color picture/' while de- 

 tails of structure are to a great extent lost (L c. 

 p. 27). The illuminating apparatus of Abbe, made 

 by Zeiss of Jena, is strongly recommended by the 

 author quoted, and will doubtless be found an 

 important aid in difficult investigations of the 

 nature indicated. For ordinary work, however, 

 a good achromatic condenser will furnish the 

 necessary illumination, and it will be found that 

 a good one-sixth or one-tenth inch objective an- 

 swers very well for this purpose. 



In order to render the number and distribution 

 of the bacteria in an organ more evident, Koch 



1 Traumatic Infective Diseases, English translation, p. 23. London, 

 1880. 



