12 ILLINOIS BIOLOGICAL MONOGRAPHS [132 



fluid is inferior to plain corrosive acetic. Other killing fluids tried were Flem- 

 ming's solution, Zenker's fluid, Kleinenberg's picro-sulphuric, formalin 

 and other less known fluids. The best preparations so far have been 

 obtained with corrosive acetic when the solution was used at a temperature 

 of from 40 to 60° C. The glycerol-alcohol mixture recommended by Looss 

 for killing nematodes yields specimens as flat as ribbons and bearing no 

 resemblance to Gordiacea. 



For killing infected hosts the solution of Camoy and Lebrun consisting 

 of equal parts of absolute alcohol, chloroform and glacial acetic acid satur- 

 ated with corrosive sublimate was found to give very excellent results. 

 It could not be used for killing Gordiacea because it made the material 

 collapse nearly as badly as did the glycerol-alcohol mixture. 



The methods of preparing the material for microscopic study were more 

 easily devised as it was possible to take up this problem at convenience. 



The ordinary methods of dehydration, clearing and imbedding were 

 found to yield nothing but flattened, torn and distorted preparations. In 

 delicate specimens at certain stages a sudden increase of one per cent in 

 the concentration of the alcohol caused excessive flattening and distortion. 

 It was therefore necessary to use an apparatus for insuring the gradual 

 changing of the liquids in dehydrating and clearing. Several devices for 

 this purpose have been introduced by European workers. The one best 

 known in this country is the differentiator introduced by N. A. Cobb for 

 making microscopic preparations of free living nematodes. This apparatus 

 is made possible by the fact that successive layers of alcohol of increasing 

 strengths can be introduced into a narrow glass tube without mixing. By 

 stirring up the tube a little it is possible to obtain a column of alcohol 

 gradually increasing in strength from the bottom upward. If the specimen 

 is placed in the bottom of the tube and the alcohol permitted to ooze out 

 thru a capillary point, it is possible to draw over this specimen a stream of 

 alcohol of gradually increasing strength. 



The apparatus used for this work depends upon a slightly different 

 principle. When alcohol is introduced at the bottom of a broad tube filled 

 with alcohol of a lower strength there is a certain amount of mixing of the 

 two liquids. Such a tube can be used as a mixing chamber. The essential 

 parts of the apparatus used consist of a reservoir, the mixing chamber and 

 the specimen chamber. The reservoir is a tube about 2 cm. in diameter 

 and 25 cm. long. It is supplied at the bottom with a rubber stopper thru 

 which a piece of small glass tubing leads nearly to the bottom of the mixing 

 chamber. The best results are obtained when this glass tube is drawn out 

 so as to leave an opening of not more than 2 mm. at the bottom. The 

 mixing chamber consists of a piece of glass tubing about 1.5 cm. wide and 

 5 cm. long supplied at each end with a perforated rubber stopper. From 

 the bottom of this chamber a piece of narrow glass tubing leads to the top 



