1923] Kessel: Experimental Infection of Rats and Mice 421 



material containing cysts of E. dysenteriae and C. hifidiri. It was 

 possible, on account of the presence of the barium sulphate, to deter- 

 mine that the substance fed passed to all parts of the digestive tract. 

 The animals were autopsied fifteen hours after feeding and exam- 

 inations were made of the intestinal contents at different levels. The 

 table on page 420 records the results. 



DISCUSSION AND CONCLUSIONS FEOM TABLE 7 



1. Both dead and normal cysts of human intestinal amoebae may 

 be found shortly after feeding in any part of the intestinal tract of 

 the experimental rats and mice. 



2. Motile amoebae were found most commonly in the caecum, 

 none being found in the small intestine. Motile forms were found 

 only once in the colon. This indicates that the caecum is the region 

 where the amoebae escape from the cyst, especially as a budding cyst 

 of Councilmania lafleuri was found here, there being but one nucleus 

 left in the cyst. 



3. The motile amoebae encountered varied greatly in size and 

 were rounded up in most instances. They often presented an uneven 

 margin and abnormal vaeuolation, indicating that disintegration was 

 in progress. It is probable that this apparent excessive rate of dis- 

 integration of motile amoebae is the result of the process of adjust- 

 ment to the environment of the new host. Some normal amoebae 

 were found. 



C. DISCUSSION 



I. Specificity of Parasites to a Given Host 



In the historj' of parasitology two opposing opinions have been 

 evident ; one, to regard parasites as being restricted to specific hosts, 

 and the other, to regard as possible in nature the transfer of a para- 

 site from one species of host to another. The first tendency has led 

 to the formation of a great many new species on the basis of their 

 habitat and has minimized, in the minds of the scientific world, the 

 danger of transference of parasite from host to host. Until recently, 

 the second tendency has been greatly underestimated, much of the 

 experimental work recorded indicating that the transference of a 

 given parasite from one species of host to another is often difficult 

 to accomplish. 



