and Laboratory Methods. 2399 



sion and so hardened again. They were then soaked in 50 per cent, alcohol to 

 prepare them for borax carmine, and then stained for one day in borax car- 

 mine. The point here is to overstain them very strongly and then to draw 

 the color as desired with acidulated alcohol. For the decolorizing it is 

 commonly recommended to use 2 per cent, hydrochloric acid in 50 per 

 cent, alcohol. But I find it preferable in decolorizing whole objects to use 

 a much stronger solution of the acid, which works more rapidly and so 

 decolorizes the surface parts quickly and before the inner organs have been 

 much affected, leaving the organs within more conspicuous than they would be 

 if the whole organism were decolorized slowly. The action of the acid must be 

 checked constantly by submitting the specimen to microscopic examination ; the 

 best results are only obtainable by carrying on the whole decolorization on the 

 stage of the microscope and under one's eye all the time. Experience will soon 

 teach one when the coloration is most satisfactory. It is also to be remembered 

 that specimens to be mounted in balsam will need to be more deeply colored to 

 compensate for the superior translucency of the specimen after clearing. After 

 this the usual technique is followed, dehydrating, replacing alcohol with oil, and 

 mounting in balsam. 



Where it is possible to get living material which it is desired to study after 

 treatment with reagents, it is very much better to compress it while still alive 

 and then kill under compression. I have found that I have had the most satis- 

 factory results in studying Cotylaspis and other flukes by using saturated aqueous 

 corrosive sublimate solution as a killing fluid. I have proceeded in the follow- 

 ing way : First the fluke is located on the slide and nearly all the water surround- 

 ing it removed with a piece of bibulous paper ; a cover-glass with a drop of the 

 sublimate solution in the center is inverted over the worm and suddenly let 

 down. The amount of the solution determines the amount of compression, but 

 as the animal does not harden instantly the compression can be somewhat regu- 

 lated, after the cover has been lowered, by additions or withdrawal at the edge. 

 This should be managed while the specimen is being viewed under a low power 

 to determine just the point of compression desired. Specimens thus killed under 

 compression are afterward hardened in serial alcohols and preserved in 70 per 

 cent, alcohol till needed for study, when they are stained, dehydrated, and 

 cleared in the usual way. This method, successfully applied, will give one won- 

 derfully clear and distinct views of the internal structure of a trematode. It can 

 be applied to the study of certain organs of other forms or to whole animals. 



Henry Leslie Osborn. 

 Biological Laboratory, Hamline University. 



