REVIEW OF THE GOLGI METHOD. 79 



" The proper duration of immersion for the pieces to obtain 

 that degree or particular kind of hardening which is best fitted to 

 secure, when they are laid in the silver solution, a fine and dif- 

 fused action upon the various elements of the nervous system 

 varies according to various conditions. These are the strength of 

 the fluid, the condition of the pieces, the quantity of fluid, tem- 

 perature, and, consequently, the time of the year. 



" The difl'erences arising from the strength and quantity of the 

 fluid may be eliminated by paying strict attention to the strength 

 of the fluid, by using covered vessels, and preserving the same 

 ratio between the number of pieces and quantity of fluid. 



" The influence of temperature upon the results of the reaction 

 is more important ; indeed, practically, all the uncertainties of the 

 method depend upon this. For example, to mention extremes, 

 good results (which, with the progressive changes, of which I shall 

 speak later; continue to appear and extend) can be obtained in 

 the warm season after an immersion of fifteen to twenty days and 

 seldom after thirty to forty or fifty days ; on the other hand, in 

 the cold season, good results are scarcely obtainable after an 

 immersion in bichromate of less than one to one and a-half 

 months. The reaction (with the progressive accompanying 

 changes) may then continue to manifest itself for two, three, or 

 four months, provided, of course, the pieces are preserved accord- 

 ing to the rules given above. It is almost superfluous to say that 

 during the gradual change from the warm to the cold season and 

 vice versa corresponding changes in the appearance of the reaction 

 take place. It is not easy to remedy these temperature changes, 

 especially because these changes of environment are united with 

 the other causes of uncertainty mentioned, and so act that obser- 

 vations made upon one series of pieces never agree closely with 

 those made upon another series. A warm chamber, of which I 

 shall speak later, cannot bring about the accuracy sought for. 



" The surest means of remedying these inconveniences is the 

 persevering repetition of the process — i.e.^ one must have a good 

 number of pieces available, bring several from time to time into 

 the silver solution, and then ascertain whether they are in the 

 desired condition. If a good reaction has taken place, one con- 

 tinues the trials at regular intervals in order to obtain all the stages 



