138 PEACTICAL PABASITOLOGY 



the glass tube into either the main excretory duct, which lies in the 

 middle of the hinder half of the body ; or into the excretory aperture, 

 which is situated in the centre of the posterior margin. In either case, 

 there is considerable danger of piercing the thin wall of the excretory 

 duct, though the point is of no great importance, as a certain portion 

 of the system is bound to become filled. 



Objects which have been successfully injected should be stretched 

 with the finger, fixed in alcohol between two glass slides, cleared, and 

 mounted in balsam. 



The organs containing yolk-cells (yolk-glands, yolk-ducts, and 

 uterus) may be made to show up very distinctly by laying fresh flukes 

 in Miiller's mixture between two glass slides, and allowing them to 

 soak until the yolk becomes brown. As soon as the parasite is fixed, 

 the upper glass slide should be removed, either for a time or altogether, 

 in order to allow the fixing fluid to act upon the surface of the body. 

 The specimens are rinsed in running water, or in water that is fre- 

 quently changed, dehydrated by means of the alcohol stages up to 

 90 per cent, alcohol, cleared in creosote, and mounted in balsam. 



The genital organs will be best seen if the worm is well pressed 

 between two glass slides and treated with Hofer's mixture. The upper 

 glass slide must be lifted from time to time, in order that the fixing 

 fluid may have access to at least one of the body surfaces. The further 

 treatment is carried out by the method described on pp. 99-100. 

 The specimens must be very carefully dehydrated and should be 

 stained with alum-carmine. Over-staining is counteracted by twelve 

 to twenty-four hours' soaking with water, followed by dehydration, 

 clearing, and mounting in balsam. 



Specimens intended for section cutting should be laid upon a glass 

 slide, stretched with the finger, and fixed by pouring hot sublimate or 

 other fixing fluid over them. They should be put through the alcohol 

 stages and then divided transversely at the level of the transverse 

 yolk-ducts. The two portions should be stained through with picro- 

 carmine this will take about twenty-four hours the superfluous 

 colour being afterwards rinsed out in water. They are then dehy- 

 drated by carefully graduated alcohol stages to absolute alcohol, 

 cleared in turpentine or xylol (very inflammable), and embedded in 

 paraffin. The finished specimens should be attached to the glass with 

 collodion clove oil ; but if the sections are to be further coloured after 

 cutting, they should be attached to small cover-glasses by means of 

 water, which is allowed to evaporate upon a thermostat. 



To obtain a minute knowledge of the structure of the liver-fluke, 

 transverse and longitudinal sections in series should be prepared from 

 several individuals. The beginner will find it sufficient, however, to 

 prepare single sections from certain parts. Such are : transverse 



