CROSS-INFECTION EXPERIMENTS 93 



be passed down the esophagus slowly until its entrance to the 

 stomach is insured. Care must be taken that it does not enter the 

 trachea. For this reason as large a catheter as can be passed com- 

 fortably should be used. Once the tube is in position, the syringe 

 without plunger is inserted and filled with the required number 

 of cubic centimeters of dilute fecal matter. The plunger is then 

 inserted, and the infective material forced slowly into the stomach. 

 When feeding material from culture, e.g., Trichomonas, it may 

 not be necessary to use the plunger as the culture fluid often 

 passes to the stomach directly without force. By this method re- 

 gurgitation is prevented and a uniform amount of material is as- 

 sured each animal. When infection is attempted by rectum the 

 French catheter and Luer syringe may also be employed. 



It is generally assumed, though not definitely proved, that en- 

 cysted stages, rather than the trophozoite stages of the intestinal 

 protozoa of man, are the usual stages that function in establishing 

 infection. Excepting Trichomonas, cysts, then, will ordinarily be 

 given by mouth, and trophozoites by rectum. Plugging the rectum 

 with a celloidin plug and bowel ligation to induce stasis has been 

 used with success by a number of investigators in infecting kittens 

 with amoebae, but this method is quite unnatural and should not 

 be employed in attempts to establish natural host-parasite relation- 

 ships between animals. 



SPECIFIC PROBLEMS AND METHODS 



The animals thus far used in animal-infection experiments by 

 the writer are listed below. The infections found in these animals, 

 together with the methods employed in working with each animal 

 and certain current problems related to each, are discussed. 



I. RATS AND MICE 



Endamoeha muris, Grassi, 1881, was the first amoeba described 

 from rats and mice. Wenyon (1907) gave us the first careful de- 

 scription of this amoeba. Brug (1919) later records finding it in 

 wild rats in Java and discusses its morphology. Hegner (1926a) 

 describes trophozoites of E. dipodomysi from the kangaroo rat. 

 Kessel (1924a) noted the similarity of the amoeba of the rat to 

 Councilmania lafleiiri (Kofoid and Swezy, 1921) in that the tro- 

 phozoites form hyaline pseudopodia, the nuclei in the resting stage 

 exhibit dispersed karyosomes and buds are produced when the 



