GENERAL METHODS, II 



formed. The solution, filtered from the precipitate, can be 

 diluted with water before use (cf. Strasburger, I, 632). 



Eau de Javelle acts like chloral hydrate, but has the ad- 

 vantage that it destroys chlorophyll much more quickly. 

 It may also be used to decolorize dried parts of plants. 



B. PHYSICAL CLEARING METHODS. ' 



13. Physical clearing will evidently be the more complete 

 as the refractive index of the enclosing fluid approaches 

 that of the cell-membrame or of those constituents of the 

 cell-contents which are concerned. Thus in many cases 

 glycerine must exercise a certain clearing effect, since the 

 refractive index of pure glycerine (1.46) is markedly higher 

 than that of water (1.33). A much more complete clearing 

 is, however, obtained by various ethereal oils, balsams, and 

 resins. Among these Canada balsam plays the chief part 

 at present, and we will therefore first describe in detail the 

 transfer to this medium. This requires, when one has the 

 object in water, a series of manipulations. 



Thus, as Canada balsam is quite insoluble in water, a 

 complete dehydration of the object is first necessary. Since 

 this is commonly accomplished with alcohol, with which 

 Canada balsam does not mix, the replacement of the alcohol: 

 by a fluid which will mix with Canada balsam, xylol, clove- 

 oil, or the like, is required. 



In this method, which may be termed the normal or ordi- 

 nary method of transfer from water to Canada balsam, three 

 distinct manipulations are to be distinguished : dehydration,, 

 replacement of alcohol, and transfer to the enclosing me- 

 dium. Whenever in the following pages transfer to or 

 clearing in Canada balsam is mentioned, the use of this 

 method, which may perhaps seem somewhat complicated to 

 beginners, is understood. After the description of the de- 

 tails of this method, we shall see that the same object can be 

 accomplished by various other methods, whose use is neces- 

 sary in some cases ; for example, when the nature of the 

 stain forbids the treatment of the preparations with alcohol. 



