i6 



ZOOLOGY FOR MEDICAL STUDENTS. 



CHAP. 



vacuoles containing the starchlike substance glycogen (Fig. 6, A ; 2, g) 

 and rodlike masses of chromatin-like material (Fig. 6, A, 2, ch). The 

 Amoeba now rounds itself off and secretes over its surface a thin mem- 

 branous protective cyst. The cyst is most frequently between n ft, and 

 14 n in diameter, but there is a wide range of variation in size, for races 



ch. 



n. 



9- 2 



FIG. 6. 



Amoebae from the intestine of man. A, Entamoeba histolytica ; B, E. coli. 



(From drawings by M. W. Jepps.) 



/;, i nested vegetable cell (Blastocystis) ; b. ingested bacteria ; ch, chromatoid bodies ; e, ingested 

 blood-corpuscles ; g , glycogen vacuole ; n, nucleus. 



of the parasite have been found in which the diameter is as small as 5 //, 

 and others in which it is as large as 20 /z. 1 



1 In the case of E. coli there exist similar differences so that, although there is 

 a tendency for the cysts of E. coli to be larger than those of E. histolytica, mere size 

 does not afford a trustworthy criterion for distinguishing between the cysts of the 

 two species. 



