PARASITES 



359 



If Sarcosporidia appear in laborator>' mice, the infection can be prevented 

 from spreading by barring any cannibalism on the part of the mice. The 

 spores are imbedded in the muscle tissue, and they give rise to infection when 

 ingested by a susceptible host. 



Helminths 

 Trematoda 



Although there can be found in the literature descriptions of trematodes 

 occurring in the house mouse, Musmusculus, it would seem highly improbable 

 that any would be found infesting laboratory mice, in 

 view of the fact that they commonly employ some 

 species of snail in which to complete their life cycles. 

 However, laboratory mice can be infested with certain 

 species of trematodes, thus, in some instances supplying 

 convenient aids in life cycle studies. Such an example 

 is reported by Price (30). 



In her life cycle studies of the blood fluke 

 Schistosomatium douthitti (Cort), Price found that the 

 adult would thrive in Mus musculus although she 

 considered Microtus pennsylvanicus as the natural host. 

 In her experiments in which M. ww5cw/m5 was employed, 

 the life cycle of the parasite was revealed. It was 

 found that the adults of the species live in the hepatic 

 portal veins of the mouse. The gravid females make 

 their way to the small veins of the intestinal wall 

 and there deposit their eggs. The eggs rupture 

 through the lining of the intestine and pass to the exterior with the feces. 

 After development in the snail, the cercariae reinfect mice by penetrating the 

 skin of the host and passing along the blood stream to the hepatic portal 

 veins where they reach maturity. 



Cestoda 



Probably the most important of the worms which may parasitize labora- 

 tory mice are the tapeworms. Some live in the mouse as adults infecting the 

 intestine or bile duct, while others employ the mouse as an intermediate host 

 and live in the liver or mesenteries. Stiles and Hassall (38) list for the house 

 mouse as many as 14 different species, obviously some of which occur so 

 rarely as to be of little importance. Five species including the more com- 

 mon and more interesting ones are discussed here. 



Fig. 140. — Strob- 

 ilocercus of Taenia 

 taenia eformis . (From 

 A ngustine.) 



