PARASITOLOGY. 221 



If alcohol be used then the parasite should be 

 placed in a 25% solution for one week. Then a 50% 

 solution for one week. Then a 75% solution for one 

 week. Then absolute. Alcohol has a tendency to 

 shrivel the tissues of round worms. Formalin has a 

 tendency to expand or swell the tissues, hence some 

 worms, as the Stephanurus Dentatus, have a tendency 

 to rupture at the genital or anal openings, if too 

 strong a solution be used. 



For museum purposes the smaller specimens can 

 be placed between two glass slides held together 

 with silk thread tied together at each end and placed 

 in an upright position in the fluid. The back slide 

 should be covered with black shellac and allowed to 

 dry before being used. 



TO STAIN AND MOUNT ENTOZOA. 



When collecting worms for laboratory study they 

 should be immediately placed in the following solu- 

 tion : 



50 parts of 70% alcohol. 



50 parts aqueous solution bichloride of mercury. 



A few drops acetic acid. 



The parasite thus killed and preserved should then 

 be washed in a gentle stream of water for several 

 hours. Then place in 25% alcohol for twenty-four 

 hours; then absolute. The parasites stain with 

 either alcoholic eosin or picric acid stains ; hema- 

 toxylin or methylene blue can be used for secondary 

 stain if desired. After staining the desired shade (the 

 time of which varies with the species of worm) the 

 specimen should be clarified in xylol, oil cedar or 



