62 THE AMERICAN MONTHLY [March, 



supported hypothesis which would be of practical use as one to w^ork 

 with, although I do not by any means wish to diminish the scientific 

 value of having such a working hypothesis. I have thus contented 

 myself with paying attention to the clearer and intelligible physical 

 processes, and not without result. Starting from the supposition that 

 the stain deposits itself in the interior of the tissues as such, and that it 

 is fixed in it in different ways in different parts, according to the reac- 

 tion thereof, I always give the preference to those methods which 

 differentiate in a way most sparing of the tissue. On the supposition 

 that many bacteria, c- g.^ tubercle bacilli, take the stam with difficulty, 

 one believed that one was able to remedy this defect by a long staining 

 (twenty-four hours and longer) , as well as by an increased temperature 

 of the staining fluid, but we must recollect that by such procedures 

 the tissue is so over-stained that the selective staining is very diiiicult, 

 and the deep staining of the bacilli is quite illusory, even if we over- 

 look the direct disadvantage of damage to the tissue. My opinion is 

 that the difficult stainability of some bacteria in tissues generally is not 

 proved ; indeed the ease with which they take up the color in dry 

 cover-glass preparations militates against such a view. In cases where 

 failure results from staining for a short time, the fault lies in the pro- 

 cess of differentiation being improperly applied. Any one may con- 

 vince himself of the truth of this by staining sections containing 

 different bacteria in weak solutions without applying means of dif- 

 ferentiation, or by treating them as though they were dry cover-glass 

 preparations. Such considerations make it appear most advantage- 

 ous not to stain too deeply, and to seek some indifferent medium 

 for extracting the color which will spare the tissue as much as pos- 

 sible. Such I have found among the aniline dyes themselves. At 

 first I considered the acid staining matter only of much practical value 

 for this purpose ; later on I found among the basic ones some with sim- 

 ilar properties. 



I found a further weak point in the processes hitherto used, viz : The 

 dehydration of already differentiated sections in alcohol, by which, 

 under certain circumstances, the decolorizing properties of the ffuid 

 must have had a very bad effect. I tried to minimize this undesirable 

 accessory effect of the alcohol by adding to it some of the stain in 

 which the sections had been previously stained, and by these means a 

 part at least of the staining matter removed by the alcohol was re- 

 placed. 



Afterwards aniline oil was recommended by Weigert as a means of 

 dehydration. I now use stained or unstained alcohol only for removal 

 of the water superficially lying as it were upon the sections in order to 

 make them spread out in aniline oil. 



The alcoholic solutions of the acid stains showed themselves suitable 

 only as a means of extraction of the color from the tissues in cases of 

 bacteria, which retain the color very firmly, whilst they decolorized 

 the others just as quickly as they did the tissue itself, and were there- 

 fore of no use without further processes. In such cases I found solu- 

 tions of the acid and basic staining matters in clove oil suitable, which 

 latter I finally replaced with much advantage by aniline oil, and latterly 

 I have made use of this material only, either pure or containing stain- 

 ing matters for means of extraction, dehydration, and double staining. 



