CHAPTER XXXIV. 473 



ones can be employed, and whole brains of small animals, particu- 

 larly if some of the fluid has been previously injected through the 

 carotid or aorta. The duration of the impregnation is from two to 

 three months, but material can be left in the mixture for much 

 longer, certainly without danger and, very likely, with advantage. 



MANN (op. cit.) recommends warming the mixture to the tem- 

 perature of the incubator and diluting it to one-half the strength 

 advocated by Cox, particularly for material of adult subjects. 

 Portions of the brain measuring 1 cm. in thickness or entire brains 

 of young animals are placed by him on cotton-wool in this solution 

 and left in the incubator for twenty-four hours, when the solution is 

 changed. After a second change on the third day the vessel (which 

 should contain the mixture in proportion of 30 : 1 of the brain) is 

 sealed with vaseline and left in the incubator for at least a month, 

 but preferably for two. I find this way of carrying out the Golgi- 

 Cox method very good, but, after incubating for a month or so, I 

 prefer keeping the vessel at room temperature, and cutting after 

 another two or three months or longer. 



There is considerable difficulty in making and preserving sections 

 which ought to be made either by free hand or by means of a freezing 

 microtome after slight preliminary washing of the pieces with water, 

 and impregnating them with 20 per cent, dextrin' for one to three 

 days as suggested by Mann. 



To convert the white mercury impregnation into a black one, Cox 

 suggested treating the sections for an hour or two with 5 per cent, 

 sodium carbonate, but 5 to 10 per cent, ammonia is now generally 

 used. They are then thoroughly washed in distilled water, carefully 

 dehydrated, cleared by one of the usual ways, and mounted, without 

 a cover, either in thick xylol balsam or in the original medium 

 suggested by Cox and composed of : Gum sandarac 75 grms., 

 camphor 15, oil of turpentine 30, oil of lavender 22-5, alcohol 75, 

 castor -oil 5 to 10 drops. For examination, add a drop of castor 

 oil, and cover. 



897. Methods for rendering Golgi-Cox Preparations more per- 

 manent. Various authors (see SANDERS, 1898, in lilt, to A. B. Lee, 

 Vade-Mecum, 1913 ed., p. 433 ; BREMER, Anat. Rec., iv, 1910, 

 p. 263) have proposed washing tissues treated according to Cox's 

 process in many changes of alcohol, and embedding them in celloidin 

 this chiefly with the object of overcoming the difficulty of cutting 

 brittle pieces by means of the freezing microtome, and also of render- 

 ing preparations more permanent by removing the excess of corrosive 



