ANIMAL PARASITES 103 



sitate hydration to water before staining. The usual grades used 

 are 70, 50, 35 per cent and water. 



Stain intensity is largely a matter of the particular structures 

 to be brought out. The best results are obtained by over- 

 staining and differentiating in acidulated alcohol (2 per cent HC1 

 in 70 per cent alcohol). Large specimens may be left in the 

 stain overnight; for smaller specimens an hour will suffice. 



Dehydration is accomplished by passing specimens through a 

 series of graduated alcohols: 70, 80, 95 percent. Large specimens 

 should be left in each grade for an hour, with a change to fresh 

 95 per cent alcohol for a second hour. They are then transferred 

 to carbol-xylol until thoroughly cleared, and mounted in Canada 

 balsam or damar. 



In mounting, each slide should include scolex, mature and 

 gravid segments, and developing segments. 



Sectioning. — Satisfactory methods of sectioning are included 

 in all manuals on microscopic technique. For general studies 

 sections may be made from specimens stained in toto. Detailed 

 histological studies necessitate staining after sectioning. The 

 usual paraffin method is most suitable. 



References 



Baylis, H. A., 1922. Notes on the collection and preservation of parasitic 



worms. Parasitology, 14 : 402-408. 

 Meggitt, F. J., 1924. On the collection and examination of tapeworms. 



Parasitology, 16 : 266-268. 



TREMATODA 



Collection. — Trematodes are to be sought in a wide variety 

 of locations in the animal body. Adults may occur in the liver, 

 intestine, bladder, lungs, and blood vessels; while the encysted 

 larval forms occur on the various organs, in the body cavity, 

 intramuscularly, and, among other places, in the eyes of various 

 hosts. Monogenetic species are to be found most commonly 

 on the gills or at the base of the fins of various fish. 



The presence of liver flukes is often most readily revealed 

 by examination of the gall for eggs. Similarly scrapings of the 

 trachea will betray the presence of lung trematodes (or nema- 

 todes). The liver should be cut into small pieces which are 

 squeezed in water. Frequently the worms will emerge if the 

 pieces are left standing in warm water. Trematodes of the 

 digestive tract are often overlooked on account of their small 



