146 BACTERIOLOGY. 



The section must be lifted from one vessel to the 

 other by means of either a curved needle or a glass rod 

 drawn out to a fine end and bent in the form of a curved 

 needle. 



By the above process of staining, which can be prac- 

 tised as a general method for most bacteria in tissues, 

 the nuclei of the tissue cells, as well as the bacteria, will 

 be more or less deeply stained. 



Special Methods of Staining Bacteria in 

 Tissues. — For purposes of contrast stains it some- 

 times becomes necessary to completely, or nearly com- 

 pletely, decolorize the tissues and leave the bacteria 

 unaltered in color. For this purpose special methods 

 depending on the staining peculiarities of the bacteria 

 under consideration have been devised. 



Gram's method loith tissues. One of the most commonly 

 employed diiferential stains is that of Gram. In gene- 

 ral, it is practised in the way given for its employment 

 on cover-slip preparations with some slight modifications. 



In this method the sections are to be placed from 

 water into a solution of aniline-water gentian-violet, 

 as prepared by the Koch-Ehrlich formula, but which has 

 been diluted with about one-third its volume of water. 

 In this the sections remain for about ten minutes, prefer- 

 ably in a warm place, at a temperature of about 40° C. 

 They should never, uuder any conditions, be boiled. 



From this they are washed alternately in the iodine 

 solution and alcohol, occasionally renewing the stained 

 with clean alcohol, until all color has been extracted 

 from them. They are then brought for one minute into 

 a dilute watery solution of eosin or safranin or into picro- 

 carmine ; again washed out for a few seconds in alcohol, 

 and finally for one-fourth minute in absolute alcohol. 



