492 Universitjj of California Publications in Zoologij 1^'cl. -O 



MATERIAL AND METHODS 



Culture albino mice, Mus musculus Linnaeus, obtained from four 

 different colonies, and culture rats, Rattiis norvegicus (Erxleben), 

 were used. The colony of rats from which oiir stock came was started 

 in 1911, when Professor J. A. Long crossed three albino females, 

 obtained from the Wistar Institute, with a wild brown male, pre- 

 sumabl}' Rattus norvegicus, caught in Berkeley. New commercial 

 .stock of albinos has been added once to this colony. Huber (1915), 

 quoting Donaldson, concluded that the albino rats from the rat colony 

 of the Wistar Institute of Anatomy and Biologj' belong to the species, 

 Mus norvegicus albinus (Donaldson). Dr. Joseph Grinnell, of the 

 California Museum of Vertebrate Zoologj', has identified an adult 

 brown rat taken this year from our stock colony as Rattus norvegicus. 



To determine the presence of amoebic infection in the culture 

 animals, the normal faeces from the rats and mice were at first 

 examined daily. This method proved to be slow, tedious, and inac- 

 curate (see Brug, 1919, and Kessel, 1923a). Successful attempts were 

 then made to evacuate the amoebae in the faeces in greater quantities 

 by the administration of a purgative, epsom salt, as described by Kessel 

 (1923a), and this method was used throughout the investigation. 



Preliminary examinations were made of all material in fresh 

 smears, one-half of the cover-glass preparation being smeared in 

 normal salt solution, the other half in Donaldson's iodine-eosin stain. 

 The active forms are easily detected in the normal saline solution, 

 while the cysts are more readily seen in the stained portion. Per- 

 manent slides were made by fixing the material for two minutes in 

 Sehaudinn's fluid heated to 60° C. The slides were stained in iron- 

 haematoxylin. 



The activity of the motile forms has been observed in normal saline 

 on an electric warming stage at 37° C. 



