III, 2. Minot: Notes on Histological Technique. 177 



kept in 70 % wliicli is changed from day to day uiitil it no longer 

 takes a brownish discolouratiou from the acid. 



6. Methods of staining. The iise of Beale's carmine has 

 come greatly iu favour. The details of the method as now followed in 

 my laboratory are given in füll in Dr. Whitman's „Methods" p. 38 — 39, 

 and therefore need not be repeated here. 



A neutral carmine Solution is very readily made as follows: — 

 dissolve the carmine with ammonia; allow the Solution to stand in a 

 shallow dish together with a dish contaiuing acetic acid, both dishes 

 being covered by a bell-jar. In a day or two the neutralization will 

 be complete; the process is more rapid the larger the exposed surfaces 

 of the liquids in proportion to their bnlk. 



The best strength of an alcoholic eosine Solution for staining is 

 about 0-0005. Dissolve 0-5 g eosine in one litre of 95% alcohol; or 

 dissolve one gramme in 100 cc alcohol, and for use dilute one part of 

 the stock Solution with 20 parts alcohol. 



Weigert's haetnatoxijline methods are applicable to sections, 

 giving at least equally good results as are obtaiued with in ioto staining. 

 They may be employed with sections of tissues hardened in various 

 ways, and need not be confined to MtjLLER's fluid or chromic acid 

 specimens. The sections are soaked first in a salt Solution for 10 to 

 15 minutes. The following aqueous salt Solutions seem to be the most 

 valuable; alum, 2 % ; chromic acid, 1 % ; bichromate of potassium, 5 % ; 

 acetate of copper nearly saturated. After soaking in one of these, the 

 section is passed quicHy through distilled water, and placed at once in 

 Weigert's haematoxyliue (1 part of the crystals in 10 parts alcohol 

 plus 90 parts water) and may be left a short time for direct colouration, 

 then washed and mounted, or a longer time imtil they become black 

 and are to be washed out by Weigert's iron Solution (water 100, 

 borax 2, ferricyanide of potassium 2%). The sections ought to be 

 moved about constantly in the iron Solution otherwise the colour will be 

 extracted irregularly. The copper haematoxyliue goes out very rapidly, 

 so that with that stain it is better to dilute the iron Solution with twice 

 its bulk of water before placing the sections in it. After the iron Solution 

 the sections must be washed very thoroughly in water, to avoid further 

 fading out, from which one is not entirely secure until the sections are 

 actually mounted in baisam. These methods are all merely modifications 

 of Weigert's, Haidenhain's and Bgehjier's methods. 



7. Picric acid carmine. There are nearly as many recipes 

 for making picrocarmine as there are writers on histological technique, 



