THE PATHOGENIC RHIZOPODA 293 



evidence of their protozoan nature. Such is the situation at the pres- 

 ent time in regard to the inclusions found in trachoma, molluscum 

 contagiosum, hydrophobia, and smallpox, while those in dysentery 

 (although still in dispute as to etiology) are universally recognized as 

 ameboid organisms. In the present chapter, I purpose to give some 

 of the evidence upon which the protozoologist bases his conclusions 

 that the more questionable inclusions referred to are actually organ- 

 isms of the rhizopod type, and if, thereby, I am able to impart some of 

 my personal convictions in regard to them, the matter of etiology will 

 take care of itself. 



In order to provide a basis for comparison of these disputed organ- 

 isms it is necessary to consider first the variations in structure that 

 occur during the life histories of widely different types of rhizopods, 

 and then to show that, despite the minor differences, they all conform 

 to a common type. The full life histories of many different kinds of 

 rhizopods have been worked out on free living material, so that there 

 is no ground for cavil as to whether such types are living organisms 

 or artefacts. 



As fully shown in Chapter III, the life histories of free living 

 rhizopods, involving many form changes, are characterized, at certain 

 periods of maturity, by diffusion of the nuclear material throughout 

 the cell and by the formation of exceedingly minute gametes. 



The curious diffuse idiochromidia are known to be no artefacts, nor 

 abnormal features of the cell, but specific and highly important 

 elements whose chief function is in sexual reproduction. It may be 

 expected, therefore, and reasonably so, that similar structures should 

 be characteristic of parasitic as well as of free living rhizopods, and the 

 idiochromidia of chlamydophrys, of entameba, of neuroryctes, and 

 cvtoryctes, features of these organisms which many observers are 

 reluctant to regard as evidences of organic structure, have the same 

 importance as elsewhere. It is upon this feature of these organisms 

 that we may reasonably depend for the assurance of the protozoa 

 nature of the cell inclusions in trachoma, molluscum contagiosum, 

 rabies, and smallpox. 



There is no reason to believe that the life cycle of a parasitic 

 rhizopod should be essentially different from that of a free living 

 form, unless, indeed, there may be an acquisition of some special 

 means of overcoming the unfavorable condition of parasitic life, such 

 as exposure to antibodies, acids, alkalies, etc., in the body fluids of the 

 host, or to difficulties in transmission from one host to another. These 

 are, in the main, provided for by the phenomenon of encystment, the 

 organism within its cyst being amply protected against unfavorable 

 conditions. Such a function, however, is shared with the free living 

 rhizopods, encystment playing an important part in the life history 

 of both shelled and shell-less forms. 



