NEUROLOGICAL METHODS. 417 



therein for from three or four to eight or ten days, and 

 finally impregnated with silver, and subsequently treated 

 exactly as in the rapid process. 



The reasons for which GOLGI prefers this process are the 

 certainty of obtaining samples of the reaction in many stages 

 of intensity, if a sufficient number of pieces of tissue have 

 been operated on ; the advantage of having at one's dis- 

 position a notable time some twenty-five days during 

 which the tissues are in a fit state for taking the silver, and 

 the possibility of greatly hastening the process whenever 

 desired by simply bringing the pieces over at once into the 

 osmic mixture ; lastly, a still greater delicacy of result, 

 especially remarkable in the demonstration of the " func- 

 tional " or nervous process of nerve cells. 



747. Critique of GOLGI'S Method. The above-described 

 methods have been found extremely valuable in the most 

 various departments of nervous anatomy. They have given 

 brilliant results in the study of peripheral nerves and their 

 origins or terminations, and in the study of the relations of 

 fibres and cells in the central nervous system. It has been 

 found at the same time that they have the defect of con- 

 siderable uncertainty in the production of the desired 

 reaction, and in the preservation of the stain. These defects 

 have given rise to a most elaborate discussion, which un- 

 happily has not as yet led to very satisfactory results. 



GOLGI'S method is apparently (but this is by no means 

 certain) based on the formation in the tissues of a precipitate 

 of bichromate of silver which is brown by reflected light, 

 but appears black by transmitted light. The problem is to 

 preserve this precipitate in the tissues free from chemical 

 or molecular change. And the problem is not an easy one ; 

 without special precautions the preparations will not resist 

 the processes necessary for imbedding, will not always resist 

 those necessary for merely mounting in balsam, and even 

 then may easily " go bad " after they have been mounted for 

 a short time. 



A critical review of the Golgi method by WEIGEET may be found in 

 Ergebnisse der Anatomic, v, 1895 (1896), p. 7. He thinks the precipitate 

 certainly consists of a silver chromate, but that we cannot say which. 



The method has also been critically studied by HILL (Brain, part 73, 



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