10^4] Kessel: Ainocbdc of Cidiitrc Eaf.s and Mice 525 



podial formation may be merely a difference of the moment, dependent 

 upon the immediate environmental condition. It is, however, more 

 generally accepted that the structure of the protopla.sm and the type 

 of pseudopodia formed are constant in the normal environment and 

 may be used as characters for differentiating species. 



In the amoebae previously described as para.sitic in rats and mice, it 

 is significant to note that, without exception, they have been described 

 as possessing hyaline pseudopodia. It is mentioned by every investi- 

 gator that there is a sharp line of demarcation between the endoplasm 

 and ectoplasm in the formation of pseudopodia. It seems that the 

 work has been carried on over a sufficient period of time and by men 

 of sufficiently sound methods in this line of investigation to con- 

 clude that if there had been any possibility of change from a hyaline 

 to a granular type of pseudopodium in this species of amoeba, it would, 

 at some time, have been noticed. It therefore seems from the work of 

 the pa.st and from the present investigation that the characteristic of 

 hyaline pseudopodial formation is a definite and constant general 

 character in these two amoebae, C. muris and C. decumani. 



As already quoted from Dobell (1921), the growing impression 

 is that in Endamoeba coli "no sharp line of demarcation separates the 

 ectoplasm from the endoplasm." With the exception of Rudovskj-, 

 all the previous investigators mention size as the chief differentiating 

 character between E. coli and the amoebae of the rat and mouse that 

 have been described by them. It follows that, if pseudopodial forma- 

 tion is to be regarded as a specific character, E. coli and the amoebae 

 of the rat and mouse described as Councilmaru'a murk and C. decumani 

 cannot be identical. 



The possibility that one species of amoeba may form h.yaline 

 pseudopodia at one time and granular pseudopodia at another time 

 has been constantly borne in mind during the present investigation, 

 but no evidence supporting this theory has been found in any of the 

 cases examined. One instance, which the writer considers to be a case 

 of a mixed infection, was found in which amoebae possessing hyaline 

 pseudopodia and other amoebae possessing granular pseudopodia were 

 found in the same field of the microscope. The actively motile forms 

 of the amoebae exhibiting hyaline pseudopodia in this particular 

 instance rounded up after being under observation about ten minutes, 

 and showed no further activity, while the amoebae with granular 

 pseudopodia remained active for an extended length of time. This 

 tendency of amoebae to become inactive after being in the unusual 

 environment of the normal saline smear for a short period is char- 



