4:8 THE AMERICAN MONTHLY [March, 



acid. A ^% solution should be used for this purpose, the tissues being after- 

 wards rinsed in rectified spirit, cleai^ed in clove oil, and mounted in Canada 

 balsam. 



STAINING BACTERIA. 



The profound thought which, during recent years, has been given to the 

 microbe theory of disease, and the refined investigations which have been 

 conducted in this department of pathology (or biology), have resulted in the 

 discovery of many methods of staining bacteria. Three processes, which I 

 have myself practised with success, and which I can thoroughly recommend, 

 both from their simplicity and the excellent results which they yield, have 

 already been published in this Journal.* 



DOUBLE OR MULTIPLE-STAINING. 



We now pass by an easy transition to the art of double, treble, and mul- 

 tiple-staining, or the difterentiating the various structure or tissues in a 

 preparation with different reagents. 



It is commonly but erroneously supposed that any tissue will take any 

 stain ; that this is not so ample proof can easily be given. The following 

 statements mav be considered as axioms : — 



I. A stain will color a tissue unless there is an aflinitv between the tis- 

 sue and the stain. 



3. No simple tissue will take a double-stain unless the cells composing 

 it are nucleated. In this case it is possible to stain the nucleus with one 

 color, and the remainder of the ceJl with another. 



3. If a preparation is composed of two or more distinct tissues, it can 

 easily be stained in two or moi'e colors ; but two or more colors cannot be 

 put into a preparation unless there is a tissue for each of them. 



These considerations lead to the conclusion that, as every tissue will take 

 a stain, many sections or preparations could be stained in as many colors as 

 there are tissues entering into its composition, if it were only possible to 

 isolate the action of staining reagents to each of those tissues separately. 



We have already seen that methyl-aniline yields a double stain in contact 

 with certain tissues. This property is also possessed by picro-carmine, and 

 indeed, io a certain extent^ by almost everv coloring reagent it is possible 

 to employ, though the decomposition is not so strongly marked as with the 

 two substances named. 



Picro-carmine, or picro-carminate of ammonia, was first introduced as a 

 stain for histological purposes by Ranvier. It decomposes into red and yel- 

 low, and hence is a strongly difterentiating reagent for many tissues. 



ALCOHOL PICRO-CARMINE FOR VEGETABLE TISSUES. 



The following preparation of picro-carmine is very valuable for staining 

 vegetable tissues : — 



A. Dissolve \ gramme of picric acid in 30 cc. of absolute alcohol. B. Dis- 

 solve ^-gramme of carmine in 3 cc. of strong liquor ammonia, and add 27 

 cc. of water. Add A. to B. The quantities should be measured exactly ; and, 

 if this is done, the solutions, on being mixed, will throw down no precipi- 

 tate. 



The process of staining with this solution is peculiar, and I shall therefore 

 describe it fully. 



The sections, after being bleached and washed, must be soaked in rectified 

 spirit, or preferably in absolute alcohol, for half an hour ; they are then 

 transferred to a w^atch-glass containing some of the stain, and covered to pro- 

 tect them from dust. In from fifteen to sixty minutes the staining will be 



* Dec, 1887, page 227 ; Jan., 1888, page 14. 



