SOME REMARKS ON CLARIFICATION, ETC. 205 



potassium chloride, with acetic acid for clarifying plant sections. 



Moeller, to conclude, very correctly places water at the head 

 of his list of clarifying reagents ; then follow glycerine, alkaline 

 solutions, Javelle water, and finally chloral hydrate. There 

 appears to be a difference of opinion among the authorities on this 

 last mentioned clarifier, which Schimper frequently and highly 

 recommends. Behrens, in his extensive catalogue of clarifiers, 

 calls attention to chloral hydrate " as being only useful for animal 

 preparations" without naming his authority. Moeller mentions 

 chloral hydrate (5 parts in 2 of water) as having been recommended 

 by A. Meyer, and refers to a publication of this last named 

 authority m the '' Archiv der Pharmacie," but in which chloral 

 hydrate does not appear. Moeller says, furthermore, that chloral 

 hydrate is preferable to diluted Uquids, inasmuch as it leaves the 

 fecula unchanged. 



Such is, however, not the case, for it is easy to demonstrate 

 that chloral hydrate causes every kind of starch to swell and change 

 into a pasty substance after about twenty-four hours' time. The 

 formation of this transparent paste does not in any manner inter- 

 fere with the admirable clarifying properties of chloral hydrate. 



I have used chloral hydrate (8 parts dissolved in 5 of water) to 

 a great extent myself as a clarifier for plant sections, and have 

 also recommended its use to those students interested in micro- 

 scopy at the Fresenius College in this city, and believe I have 

 thoroughly investigated its advantages and disadvantages while 

 comparing it with other clarifiers. A short communication may, 

 therefore, be acceptable on this as well as on a similar clarifier 

 lately discovered by me, and which, I think, is somewhat superior 

 to chloral hydrate. 



As already stated, Dippel has explained in a masterly manner 

 the reason for clarifying plant sections. The means for obtaining 

 this result are, i, the removal of troublesome substances, and 2, the 

 saturation of the object under examination with a body, the 

 refractive power of which is so nearly equal to that of the cell 

 walls, that the light may penetrate as much as possible ; but still 

 sufSciently different to admit of the cell walls appearing sharply 

 outlined under the microscope. The division of clarifiers into 

 chemical and physical by Zimmermann, seems to have originated 



