350 BIOLOGY OF THE LABORATORY MOUSE 



tumor but because with the tumor the animal was unable to keep his para- 

 sites in check. Deviations from the normal blood count may be due to 

 parasites rather than to the experimental factors under consideration. 



There is not only the havoc caused directly by the parasites to be guarded 

 against, but also that which they may cause more indirectly by acting as 

 transmitters for pathogenic viruses, bacteria, and protozoa. Although not 

 so many mouse diseases have been proved to be spread in such manner, it 

 seems possible that especially the blood-sucking parasites — bedbugs, mites, 

 lice, and even fleas are of much greater importance as vectors than is 

 definitely known. 



Sometimes the fact that the mouse may act as host for so many parasites 

 proves to be an advantage for the research worker. In many instances it 

 has afforded a convenient way to study phenomena of parasitism. Basic 

 principles discovered in studying mouse parasites can well be applied to 

 parasites of man or domestic animals which do not lend themselves so 

 readily to experimentation. Also, some forms pathogenic to man or domes- 

 tic animals may be caused to take up their abode in the mouse. Thus, a 

 very convenient living culture chamber is provided for the parasitologist. 



In this chapter an attempt has been made to discuss briefly many of 

 the protozoon, helminth, and arthropod parasites which may be expected to 

 be found infesting laboratory mice. ■ 



Protozoa 

 Amoebae 



Endamoeba muris (grassi, 1879). — This (Fig. 135) is probably the most 

 common amoeba found in the mouse. Of 85 house mice collected at 

 Durham, N.C., Harkema (18) found as many as 13.09 per cent harboring 

 this protozoan in the small intestine. It has also been reported as found 

 in the caecum and colon of mice and of rats. 



Structurally E. muris is very similar to E. coll. Tryphozoites will 

 average 30 fx in diameter. They display protruding pseudopodia with 

 glassy covered ectoplasm and a fine granular zone. In the cytoplasm are 

 occasionally lustrous granules. The nuclear membrane is thick with 

 peripheral chromatin granules, and there is a large karyosome. Coccal 

 bacteria may be enclosed in the cytoplasm. Cysts measure 15 tx-20 n in 

 diameter, and when mature they contain eight nuclei although two and 

 four nucleated cysts may be found. 



E. muris is probably also much like E. coli in that it is not pathogenic 

 but lives more as a commensal in the lumen of the intestine of the mouse. 



