NEUROLOGICAL METHODS. 413 



born animals at a time when the fibres have not become 

 surrounded by their sheath of myelin. 



There is no other method which will allow cell-processes 

 to be followed out for such great distances. But the method 

 does not demonstrate at the same time the histological detail 

 of other tissues that may be present in the preparations, and 

 all cytological detail is lost. It it par excellence a special 

 method. 



Nervous tissue is not the only thing that is impregnated 

 in these preparations ; neuroglia, connective tissue, fibrils, etc., 

 are impregnated, and the method has been applied with 

 success to the study of such things as bile-capillaries, gland- 

 ducts, and the like. Both on account of this character, and 

 on account of the capriciousness with which the impregnation 

 takes hold of only certain elements of the preparations, care 

 must be exercised in the interpretation of the images ob- 

 tained. As with gold impregnations, the very best prepara- 

 tions give images that are only worthy of credence as to what 

 they show, and furnish absolutely no evidence whatever as to 

 the non-existence of anything that they do not show ; for you 

 can never be sure that the imbibition of the salt has not 

 capriciously failed, or its reduction capriciously stopped, at 

 any point. And a further source of error is found in the 

 fact that the method frequently gives precipitation-forms of 

 the silver salt that simulate dendrites and other structures 

 (see FRIEDLAENDER in Zeit. f. u-iss. Mik., xii, 2, 1895, p. 168, 

 and the plate in the following number). A correspondent 

 writes me that he has " Golgified a potato, and obtained 

 beautiful nerve-fibres," and FKIEDLAENDER'S paper describes 

 similar results obtained with white of egg, etc. And other 

 workers have made similar observations. Clearly, then, 

 much caution is necessary in the interpretation of the 

 images. 



The method has been applied with success to the tissues 

 of Invertebrates Insects, Lumbricus, Tubifex, Helix, Limax, 

 Distomum, Astacus, etc. 



The details of the method have been considerably modified 

 at the hands of various workers, the most important modifica- 

 tion being that of the " double " or " intensified " impregna- 

 tion of RAMON Y CAJAL. 



The method has been described at length by GTOLGI in the 



