This is a report of a thorough investigation of the flagellated intestinal parasites of wild and tame rats and mice and of guinea pigs. In these animals in a wild state infestation is usually of a single strain, while laboratory stocks generally harbor several strains. Of the flagellates studied, only Giardia appears to be pathogenic; the others could be considered commensals. The biologic experiments are interesting. It is apparent that the character and the quantity of intestinal mucus are determining factors in the selection of the sites of infestation. A predominantly gram-positive intestinal bacterial flora is unfavorable for parasitism. The effect of the avitaminoses studied is surprising. Scorbutic guinea pigs are neither more nor less susceptible to parasitic infestation than normal animals. Animals suffering from A-avitaminosis, however, because of the diminished production of mucus, are much more resistant to parasitism than are normal animals.
Efforts to produce animal infestation with