48 HUMAN INTESTINAL PROTOZOA IN THE NEAR EAST 



different. The difficulty of diagnosis may be only overcome in 

 some instances by following a case for several days with the careful 

 examination of fresh iodine preparations as a control of the fixed 

 and stained films. 



A feature of the E. histolytica infection, which the examination 

 of a large series of cases has impressed upon us, is the variation in 

 the size of the cysts. Small forms of E. histolytica cysts have 

 been described by James, in Panama, and more recently by 

 Penfold and Woodcock. Kuenen and Swellengrebel described the 

 E. histolytica cysts as varying in size between 11 and 19 microns. 



We have noticed a similar variation in size, but it appears that 

 various strains of E. histolytica occur. There is one which pro- 

 duces very small cysts associated with correspondingly small 

 "minuta" forms of amoebae. The cysts are 7 to 10 microns 

 in diameter and have the same characters as the larger cysts. 

 These are the forms described by James and by Penfold and 

 Woodcock. The small cysts do not appear to be accidentally small, 

 but cases infected with the small strain pass small cysts regularly, 

 at any rate for some weeks, with no tendency for the small cysts to 

 be replaced by the larger ones. For instance, case Kettlewell was 

 observed for three weeks, during which a twelve-day course of 

 one-grain emetin injection was given without result, and small 

 E. histolytica cysts were found constantly. He was finally cured 

 by a course of emetin by the mouth. 



Starting from the strain with small cysts, a series of strains 

 occur with gradually increasing average size of cyst. There are 

 strains in which the cysts measure from 9 to 12 microns, others 

 10 to 14, others 12 to 16, and finally large strains with cysts measur- 

 ing 14 to 18 microns. As is to be expected, each strain is associated 

 with " minuta " forms of amoebae of corresponding size. 



It seems very improbable that these strains represent different 

 species of amoebae, for we cannot be sure that a strain of amoebae 

 which will produce cysts of small size at one time will never at 

 another time produce larger ones. We have noted, however, that 

 in case Healy, in which cysts of large average size were found for a 

 long time, towards the end of the period of observation a certain 

 number of smaller ones began to appear. The point, however, can 

 only be definitely decided by following individual untreated cases 

 for long periods. In order to illustrate this variation we reproduce 

 below a series of measurements in microns made from cysts as they 

 appeared in iodine preparations. Only cysts circular in outline were 

 measured and the cysts were consecutive ones, as they were observed 

 in working through the preparation with the ^-inch objective. 



