412 University of California Publications in Zoology [Vol. 20 



The material used for feeding was obtained from the laboratory 

 of the Division of Parasitology of the California State Board of 

 Health, which is under the direction of Professor C. A. Kofoid. The 

 diagnoses were made first by that laboratory and later authenticated 

 by the writer before feeding the rats. The morphological character- 

 istics of the amoeba common to man were compared with the descrip- 

 tions and figures of Kofoid, Kornhauser, and Swezy (1919), Dobell 

 (1919), Kofoid and Swezy (1919), and Kofoid (1923). As it was 

 not always possible to obtain a sufficient quantity of faecal material 

 to feed a large number of rats, the interval between feeding in some 

 instances is considerable. In feeding, bread was soaked in water 

 until it became quite soft. The water was then squeezed out and a 

 small handful of bread was placed in each feeding dish. The faecal 

 material was well mixed with water in another dish until it was very 

 liquid in consistency. A portion of this was then poured over the 

 bread in each dish and the contents well stirred. There was no con- 

 stant proportion of faecal material to bread, for the amount of faecal 

 material obtainable varied. The rats ate well of all mixtures fed even 

 though the bread was always colored by the faeces. 



After the feeding experiments were completed and an interval 

 of two weeks or longer had passed, the rats were examined, always 

 after being given a dose of epsom salt. Fresh smears were examined 

 in iodine-eosin and permanent smears were stained with iron 

 haematoxylin. 



II. Tables and Conclusions 



The results of the feeding experiments are displayed in tables, 

 and a short discussion follows of the conclusions drawn from each 

 table. 



DISCUSSION AND CONCLUSIONS FEOM TABLE 1 



1. Eight out of twenty-nine, or 27.6 per cent of all the rats fed, 

 became infected with E. dysenteriac. 



2. Eight out of ten, or 80 per cent of all amoeba-free rats fed, 

 became infected with E. dysenteriae. This may have been due in 

 part to their being non-infected rats, and in part to their having 

 received an extra feeding of E. dysenteriae cysts on January 5 which 

 the other rats did not receive. It will be noticed in tables 4 and 5 

 that a greater percentage of amoeba-free rats became infected than 

 was the case with rats having a previous amoebic infection with rat 

 amoebae. 



