ANIMAL PARASITES 3 



PRACTICAL WORK 



The object of this exercise is to illustrate the common types 

 and general distribution of parasites in the organs and tissues of 

 an animal host. For this purpose the frog is an exceptionally 

 favorable subject. It harbors a large number and variety of 

 entozoa, illustrative not only of the major groups but even of 

 genera of important parasites of man. The work of this 

 practicum is of a general nature, but we shall return to the study 

 of frog parasites in greater detail as we take up particular groups. 

 Lay the frog on its back on a dissecting board or tray and 

 extend and pin down the legs. Open the abdominal and thoracic 

 cavities by a median ventral incision and pin back the flaps. 

 By way of review identify the general internal anatomical 

 structures before making the special study of them for parasites. 

 Examination of the Blood.— Using slides and covers which 

 have been thoroughly cleaned in alcohol to remove all grease, 

 mount a small drop of blood. Cut down the light in the micro- 

 scope and carefully search through the entire field for blood 

 parasites. Care should be taken not to make the mount too 

 thick, thereby rendering it opaque. If necessary a drop of 

 physiological salt solution (0.75 per cent NaCl) may be added to 

 dilute the blood. 



Trypanosoma rotatorium is a flagellated protozoan found 

 free in the blood plasma. It is approximately twice the length 

 and about the breadth of the red corpuscles of the frog, moves 

 about actively, and presents marked changes in form. It is 

 rarely abundant but, if present, can usually be found in the blood 

 from the kidney. 



Lankestrella ranarum is a sporozoan which, like the parasite 

 of malaria, is found within the red blood corpuscles and blood 

 plasma of the host. In the fresh corpuscle it appears as a clear, 

 spindle-shaped body. Spindle- or crescent-shaped forms pre- 

 dominate in the blood. Another sporozoan, Dactylosoma 

 ranarum, also occurs in the red blood cells of frogs and undergoes 

 an asexual multiplication within them. If heavily infected 

 frogs are found, permanent preparation may be made as directed 

 in the Appendix. 



Blood filaria, minute larval roundworms, have been reported 

 for frogs but have not been recorded for our native species. 



Body Cavity. — Clinostomum attenuatum. — Examine the mesen- 

 teries, the peritoneum of the body cavity, and the lymph spaces 



