76 



a ]/4 C /c solution of silver nitrate, and then for 2 or more days in a 

 %% solution of silver nitrate, preferably keeping it in the dark. 

 Without washing, imbed rapidly in celloidin as follows: 

 (a) Dehydrate 2 to 3 hours in 95% alcohol, changed two or 

 three times; (b) place in thin celloidin for 20 minutes, in thick cel- 

 loidin for 20 to 30 minutes; (c) imbed in thick celloidin, on a block 

 of wood (best ; 65a) ; (d) harden the mass in chloroform for 20 to 

 30 minutes, and (e) place the block in clarifier and cut, sections 

 being 50 to 100 ^ thick according to the nature of the tissue and the 

 character .of the impregnation. 



(/) Place the sections in 95% alcohol for a few minutes; clear 

 in carbol-xylene and mount in balsam by placing the section on the 

 slide, absorbing the clearer thoroughly by means of tissue paper and 

 spreading over it thick xylene balsam. Do not cover. Later, when 

 the balsam has hardened somewhat, it may be melted by heat and 

 much of the superfluous balsam drained from the section and scraped 

 away with a knife, and a cover glass added if desired. 



207. Time oj hardening. From results of Cajal, van Gehuch- 

 ten, and others, and from general laboratory experience, the follow- 

 ing periods will probably be found approximately correct. In 

 general: The best results are to be obtained with kittens 3 to 20 

 days old, puppies 2 weeks old, rats 8 to 10 days, rabbits 8 days, (a) 

 For cerebral cortex (and hippocamp) : New-born kitten, 1 to 2 days; 

 kitten half grown (3 to 4 months), 3 to 4 days; new-born rabbit, 24 

 hours; rabbit one month old, 2 to 3 days; adult mice, 3 to 4 days. 



(b) For spinal cord : Chick of 5 to 6 days' incubation, 24 hours; 

 chick, 14 to 15 days' incubation, 3 days; new-born kitten or puppy, 



2 to 3 days. Frog tadpoles (large) 3 to 5 days. 



(c) Cerebellum: New-born kitten, 1 to 2 days; kitten half 

 grown, 4 days. 



(d) Sympathetic system: Chick of 14 to 18 days' incubation, 



3 days. 



(e) Retina : 1 to 3 days. 



(/) Olfactory mucous membrane: 3-4-7 days. 



208. Intra vitam Methylene Blue. Methylene blue shares 

 with a number of coal tar dyes the power of staining during life 

 nerve cells and fibers and certain cytoplasmic granules. Like the 

 Golgi methods, "intra vitam" staining of nervous tissue is capricious; 

 applicable only to living or fresh tissue and depends upon unknown 



