154 A REVIEW OF THE GOLGI METHOD. 



damar, which, after many comparative tests, I have found better 

 adapted for this purpose than Canada balsam. I must here call 

 attention especially to a peculiar treatment of the sections ; con- 

 trary to the usual custom, I do not cover the preparations with a 

 cover glass. When the sections are covered in the usual way with 

 a cover glass, they begin after a time to turn yellow (owing to a 

 second impregnation which takes place), then the outline of the 

 stained cell elements become obliterated, the whole tissue becomes 

 opaque, and, after a period of from two or three months to two 

 years, the preparations, with few exceptions, become useless. On 

 the contrary they may keep a long time, thanks to the repeated 

 washing, of which I have spoken, and especially to the mode of 

 mounting without a cover slip in a layer of damar. I can now 

 state that the earUer lamentable disadvantage that preparations 

 made by my method soon spoiled is now almost completely reme- 

 died. I have many preparations, made by me nine years ago, 

 which have not yet lost their original clearness. 



" If the good preservation appears menaced by an incipient 

 yellowing, another longer bath, on the slide, in turpentine will 

 restore transparency and freshness to the preparation. 



"I have found it convenient to employ for this kind of mount- 

 ing a special wooden slide with a square opening, in which, by 

 means of a groove, a glass plate (a cover slip of somewhat greater 

 diameter than usual) is fitted and stuck fast with a solution of 

 shellac in alcohol. This serves as a slide, and the section adheres 

 to it by means of the damar. 



" This kind of slide not only enables the section to be exam- 

 ined from both sides, but also has the advantage of preventing 

 dust from fouUng the object, to which this kind of mount would 

 be especially exposed. To accomplish this it is only necessary to 

 turn the side of the slide with the section downwards, as soon as 

 the damar is hard enough, or to pile the preparations on top of 

 each other. 



" I further remark that it is wise to shield the objects from the 

 influence of light ; still this precaution is not entirely necessary 

 if the repeated washing has been carefully performed. After ful- 

 filling these conditions, I might expose preparations for days to 

 the sun's rays without injury to them. 



