TEXT-BOOK OF BACTERIOLOGY. 59 



alteration of the original method of Gram, which often proves 

 serviceable. 



Gtinther stains the sections in a fully-saturated opaque solution 

 of anilin-water gentian-violet for a minute; then two minutes in 

 iodide of potassium solution, half a minute in absolute alcohol, ten 

 seconds in a 3 to 5^ solution of muriatic acid in alcohol, then once 

 more absolute alcohol, then contrasting stain, etc. The addition of 

 muriatic acid gives the alcohol the power of dissolving and remov- 

 ing the particles of coloring matter which adhere to the tissue. 



Also in the double staining by Gram's method the strong de- 

 coloring influence of alcohol is often an inconvenience. The bac- 

 teria lose their color and disappear completely from view. 



It is, therefore, frequently advisable to take anilin oil instead of 

 alcohol. Stain the section first with picro-carmine, etc., then place 

 it in anilin-water gentian-violet, next in iodide of potassium solu- 

 tion (Gram's solution), and then it must go immediately, without 

 any previous immersion in alcohol, into the anilin oil, then comes 

 oil of cloves, or xylol, and Canada balsam. All this is best done 

 on the slide. 



Never stain a large number of sections at once without having 

 proved the correctness of the whole process by one or more suc- 

 cessful trials. For almost every separate case and every staining 

 solution one should endeavor personally to find out by experiment 

 the right conditions of time, strength, heat, etc., etc. 



Precise directions as to the time, etc., for the different processes 

 have, therefore, been intentionally avoided as far as possible. 



It may seem that this is a very strange way of beginning, and 

 that if we worked with No. 1 solution. No. 2 solution, etc., and 

 always knew their exact percentage of coloring matter, we might 

 have a little chance of success. Such directions, however, would 

 only be found infallible in a restricted number of cases, and the 

 mechanical observance of such rules would sink the art of staining 

 into a mere trade. If one only knows rules for staining and not why 

 he must act so and not otherwise, he knows in truth very little. 



And yet many a person thinks he has all the secrets of staining, 

 or even the whole science of bacteriology, in his pocket, when he 

 carries home with him a few pretty red and blue double stainings. 

 Yet the immense advantages which experimental science gains 

 from the use of stained preparations will not be renounced on that 

 account. 



The finer varieties of form in the bacteria, the slight differences 

 of length and thickness, the extremely characteristic shapes of par- 

 ticular species — all this can only be demonstrated by staining. 



