and Laboratory Methods. 2*245 



CURRENT ZOOLOGICAL LITERATURE. 



CHARLES A. KOFOID, University of California. 



Books and Separates of Papers on Zoological Subjects should be Sent for Review to Charles A. 

 Kofoid, University of California, Berkeley, California. 



Looss,A. The Sclerostomidae of Horses and The nematodes are found in the coecum 

 Donkeys in iigypt. Kecoras Egypt. Gov. 

 School of Medicine. 1: 25-141, 13 pis. and large loop of the colon. In collec- 



^9°'- tion the practice was to ligature the 



gut at intervals, slit it longitudinally, and roll out the contents without disturbing 



the original position of the parasites near or attached to the intestinal wall. 



The worms should be preserved immediately upon collection, for they contract 



and wrinkle upon cooling. The Sclerostomidae, and the greater part of other 



nematodes, are easily fixed in an extended state by placing them in 70 per cent. 



alcohol, heated to 80°C. Contracted individuals will extend when placed in the 



hot fluid. A few forms, such as Trichocephalus, show a tendency to coil up 



when placed in the alcohol. This may be prevented by grasping the worm 



between the blades — not the points — of a pair of forceps and shaking out the 



coil in the killing fluid. This method of killing avoids shrinkage, and gives fine 



histological details. The worms may be kept permanently in alcohol of this 



grade. Formalin preserves these nematodes well, renders them somewhat 



transparent, but interferes with subsequent treatment by alcohol, which causes 



unavoidable shrinkage. 



For the microscopical study of the worms killed in alcohol it is necessary to 

 clear the tissues. This is accomplished by adding 5 to 20 per cent, of glycerine 

 to the 70 per cent, alcohol in which the worms are placed, and allowing the 

 alcohol to evaporate slowly. The weaker solutions of glycerine and slow 

 evaporation must be used with the more resistant species. The water should 

 also be evaporated by placing the preparations in a water bath. Small and less 

 resistant species may be placed directly in 20 per cent, glycerine solution, and 

 in a day are ready for evaporation in the water bath. Material killed in various 

 standard reagents resists the glycerine solutions, and at the best is less trans- 

 parent than that fixed in hot alcohol. Worms thus cleared in glycerine exhibit 

 their internal structure very well. The alcohol-glycerine mixtures may be 

 heated and used in place of the alcohol for fixing, thereby reducing the time in 

 preparation. Small worms killed in the 20 per cent, glycerine and placed at 

 once in the water bath are ready for examination in 24 hours. 



Worms from the pure glycerine may be brought directly into 96 per cent, 

 alcohol without shrinkage, and carried through cedar oil to paraffin. The 

 cuticle should be slit in several places to facilitate the passage from absolute 

 alcohol to oil. Cedar oil is very highly recommended by the author for clearing 

 preparatory to paraffin. It penetrates quickly without shrinkage (in incised 

 specimens) and does not cause brittleness. Sections and whole preparations 

 were mounted in glycerine gelatin to avoid the transparency caused by balsam. 



c. A. K. 



