METHODS OF OBSERVING BACTERIA. 87 



Some of the bacteria to be stained are mixed upon a 

 cover-glass with a drop of distilled water. This is the 

 first dilution, but is too rich in bacteria to allow the 

 flagella to show well, so that it is recommended to prepare 

 a second dilution by placing a small drop of distilled 

 water upon a cover and taking a small portion from the 

 first cover to the second, spreading it over the entire sur* 

 face. The material is allowed to dry, and is then fixed 

 by passing it three times through the flame. When this 

 is done with forceps there is some danger of the prepara- 

 tion becoming too hot, so Loffler recommends that the 

 glass be held in the fingers while the passes through the 

 flame are made. 



The cover-glass is now held in forceps, and the mordant, 

 Solution A, is dropped upon it until it is well covered. 

 The cover is wanned until it begins to steam, and the 

 stain replaced as it evaporates. It must not be heated too 

 strongly ; above all things, must not boil. This solution 

 is allowed to act from one-half to one minute, is then 

 washed in distilled water, then in absolute alcohol until all 

 traces of the solution have been removed. The real stain 

 Loffler recommends an anilin-water fuchsin (Bhrlich's 

 solution) which should have a neutral reaction, is now 

 dropped on so as to cover the specimen, and heated for a 

 minute until vapor begins to arise; it is then washed off 

 carefully, dried, and mounted in Canada balsam. To 

 obtain this neutral reaction enough of the i per cent, 

 sodium-hydrate solution is added to an amount of the 

 anilin-water-fuchsin solution having a thickness of sev- 

 eral centimeters to begin to change the transparent inrf> 

 an opaque solution. Such a specimen may or may not 

 show the flagella. If not, before proceeding farther it is 

 necessary to study the products of the bacterium in cul- 

 ture-media. If by its growth the organism elaborates 

 alkalies, Solution C, in proportion from i drop to i c.cm. 

 in 1 6 c.cm. of the mordant A, must be added, and the 

 process repeated again and again until the proper amount 

 is determined. On the other hand, if the organism by 



