2 University of California Publications in Zoology [Vol. 18 



I wish to acknowledge to Professor Charles A. Kofoid and to Dr. 

 Olive Swezy my appreciation of the help given me in the various fea- 

 tures of this research. 



Material and Technique 



The meadow mice were collected in fields about a mile from the 

 University campus. These fields have an abundant growth of long 

 grass in which the runways of these mice are easily found. In the 

 afternoon the common "Catch 'em alive" traps were set in these run- 

 ways, having been previously baited with crushed barley. The mice 

 were collected the following morning from the traps. 



Most of the trapping was done during the rainy season, character- 

 istic of winter months around Berkeley, and as a result many of the 

 mice were found dead from exposure in the traps. Often, however, I 

 could not make an examination of these dead mice the same day I col- 

 lected them, but waited until the second day ; even then the parasites 

 w^ere often found to be living. 



Ordinary smears upon cover-slips were employed. These were 

 made by cutting out a piece of the intestine about five millimeters long, 

 moistening it with normal salt solution, and smearing it over the sur- 

 face of the cover-glass. This was done in order to obtain the flagellates 

 which adhere to the mucous lining of the epithelium as well as those in 

 the lumen. Thin smears were prepared from faeces in the rectum and 

 colon, the material being rolled out upon the cover-slip, in normal salt 

 solution. 



The smears on the cover-slips were fixed in hot Schaudinn's fluid 

 and stained in aqueous iron haematoxylin. Mallory's connective-tissue 

 stain was also used. It was of importance in bringing out the neuro- 

 motor apparatus. The intracytoplasmic fibrils stain a bright red 

 therein, but it was not satisfactory as a nuclear stain. Counter-staining 

 with eosin made a clear differentiation between the cytoplasm and the 

 chromatin, and enabled one to trace the course of the flagella, but 

 upon the whole gave no advantage in the study of mitosis. 



The data in this paper are based on the examination of twenty- 

 three mice, all of which were Microtus calif ornicus calif or nicus (Peale) . 

 From the table given below, it will be noticed that four of the mice con- 

 tained no parasites, but that these four had been dead several hours at 

 the time the examination was made. The remaining nineteen mice 

 were infected, thus making a very high rate of infection. 



