70 W. BEVAN LEWIS. 



of the cortical layer of the brain should embrace all these 

 qualities, together with a fair view of the vascular channels, 

 whilst the delicate reticular arrangement of the surrounding 

 matrix should be unaltered by the reagents employed. The 

 difficulties in our way are great, but yet of late patient and 

 laborious investigation has rewarded the inquirer with fre- 

 quent triumphs of a most substantial character. Of the 

 numerous colouring agents used by the microscopist, the 

 more valuable for purposes of studying cerebral histology 

 are the following : carmine, logwood, picric acid, aniUne 

 blue, aniline black, magenta or rosaniline, aniline red or 

 fuchsin, and the various Judson's dyes. We owe import- 

 ant assistance also to the reduction of certain metallic com- 

 pounds by the agency of the organic germinal centres of the 

 tissues, e.ff., osmic acid, chlorides of gold and palladium, 

 oxide of uranium and nitrate of silver. The latter series 

 I shall not refer to further in this article, as my attention is 

 to be given entirely to the members of the first series, which 

 give their own natural colour to the objects exposed to their 

 action. I may, however, in passing, recommend solutions 

 of each of the latter class of the ordinary strength of one 

 per cent, to be kept in hand. 



For actual use the solutions of gold and silver may then 

 be diluted to the extent of 25 to 0-5 per cent., the chloride 

 of palladium to 0*1 per cent., the chlorides of gold and 

 potassium combined should represent in every 100 cc. of the 

 solution — voth of a gramme of the salt, whilst the osmic 

 acid solution should vary from 1 to 2 per cent, in strength. 



With this brief mention of the metallic dyes I pass on 

 to the subject more immediately concerned and describe 

 seriatim the several processes employed by myself for stain- 

 ing the cortex of the cerebrum and cerebellum. First in 

 the series is carmine, the earliest agent used for this 

 purpose. 



Carmine dyeing and its modijications. — Gerlach, with whom 

 originated the process of dyeing, used a solution of carmine 

 which has since been modified by Thiersch, Beale, and Frey. 

 The solution recommended by Beale (a carminate of am- 

 monia) is, I believe, the one most generally adopted, and 

 possesses, with some drawbacks, several points of advantage 

 over other media. The whole process of carmine-staining 

 demands, however, great attention to details to secure perfect 

 success. One essential feature is that the solution should 

 contain but a minimum amount of ammonia, and this is of 

 special importance when we are dealing with cerebral tissue. 

 Again, the after process of washing should be conducted 



