88 PARASITIC AMGEBJE OF MAN. 



diameter, but in my experience it is very rarely that 

 one of these organisms exceeds 25 to 30 microns in 

 diameter. It may be stated, as a general rule, that 

 this parasite measures from 10 to 20 microns in diam- 

 eter, while the average measurement of Entamceba 

 Mstolytica is from 25 to 35 microns. 



The difference in size between the two species is 

 of but slight value in differentiation and a separation 

 of the amoebae of the human intestine into species, 

 based upon the size of the organism, is both unscien- 

 tific and erroneous. It is one of the least valuable of 

 our methods of differentiation. 



Some authorities have stated that pathogenic 

 amoebae are always larger than Entamceba coli, but 

 I have very frequently observed cases of pure 

 infection with Entamceba Mstolytica in which the 

 amoebae were as small as the ordinary Entamceba coli. 

 As a matter of fact, both large and small amoebae are 

 present in every infection, so that it is impossible to 

 differentiate between them on account of their size. 



During the encysted stage of development En- 

 tamceba coli is much smaller than during its vege- 

 tative stage, the average diameter being from 10 to 

 15 microns. 



Shape. The shape varies with the motility of the 

 organism. When motionless Entamceba coli is spher- 

 ical or slightly oval in shape, but when in motion the 



