414 CHAPTER XXXII. 



Archives Italiennes de Biologie, t. iv, 1883, p. 32, et seq., and 

 vii, 1886, p. 15, et seq. The following account is from the 

 latter paper. The earlier form of the method should not be 

 followed. 



744. GOLGI'S Bichromate and Nitrate of Silver Method, SLOW 

 Process (loc. cit., p. 17). (a) The hardening. This must be 

 done in a bichromate solution. Either pure bichromate of 

 potash may be employed, or liquid of Miiller (the reaction 

 can be obtained with liquid of Erlicki, but it is not to be 

 recommended). The normal practice is to take bichromate 

 of potash, beginning with a strength of 2 per cent., and 

 changing this frequently for fresh solutions of gradually 

 increased strength, 2, 3, 4, and 5 per cent. The tissue to 

 be operated on should be as fresh as possible ; though satis- 

 factory results may be obtained from material taken twenty- 

 four to forty-eight hours after death/' It should be in pieces 

 of not more than 1 c.cm. or 1 \ c.cm. in size. 



The most difficult point of the method consists in hitting 

 off the exact degree of hardening in the bichromate that 

 should be allowed before passing to the next stage of the 

 process, the silver-bath. In summer good results may be 

 obtained after fifteen to twenty days, and the material may 

 continue in a favourable state for impregnation up to thirty, 

 forty, or fifty days. In cold weather good results can 

 seldom be obtained under a month ; when obtained, the 

 material may continue to give good results up to two, three, 

 and even four months of hardening. The only way to make 

 sure is to pass trial portions of the tissue at intervals into 

 the silver-bath, in summer frequently, in winter every eight 

 or ten days, and observe whether the reaction is obtained. 



Good results are obtained by injecting the organs with 

 the hardening fluid (2*5 per cent, bichromate). See 681. 



Stoving at a temperature of 20 to 25 C. is useful for 

 -abridging the hardening, but there is risk of over-hardening ; 

 and GOLGI thinks the results are never quite* so delicate as 

 after hardening in the cold. 



(b) Impregnation. As soon as the pieces of tissue have 

 attained the proper degree of hardening, they are brought 

 into a bath of nitrate of silver. The usual strength of this 

 bath is 0'75 per cent., but 0'50 per cent, may be taken for 



