2<)2 THE PATHOGENIC RHIZOPODA 



rhea. Brooks has given strong evidence to show that Bed. coli was the 

 cause of a fatal disease resembling dysentery, in some valuable apes 

 belonging to the New York Zoological Society, and from his observa- 

 tions it is evident that these ciliates must be taken into account in 

 searching for the causes of certain types of intestinal trouble, for, if 

 not themselves the direct causative agent, they may be the bearers of 

 some more pernicious organism. 



While ciliates and flagellates are not adapted morphologically for 

 an intracellular parasitic life, the rhizopods have no such disadvan- 

 tage, and by virtue of their ameboid movements, and of the cytolytic 

 ferment which they are apparently able to secrete, they make their 

 way into tissues and cells and then live upon the fluid elements of 

 the living protoplasm. Thus, Plasmodiophora brassiccs, while in the 

 young amebula stage, works its way into the root cells of a cabbage 

 or turnip plant, absorbs and grows upon the fluid protoplasm of the 

 plant cells, forms a plasmodium, and reproduces within these cells 

 (see p. 209). Certain human diseases, notably dysentery, hydro- 

 phobia, and smallpox, are characterized by the destruction of tissue 

 cells, the agent being minute ameboid forms which we interpret as 

 protozoa. In dysentery the organism causes the destruction of the 

 epithelial cells of the digestive system; in hydrophobia, the nerve cells 

 of the brain are destroyed, and in smallpox, the epithelial cells of the 

 skin. 



In none of these cases is it generally agreed that the structures 

 found within the diseased cells are the causes of the several diseases, 

 and, indeed, in the last two, hydrophobia and smallpox, pathologists 

 do not agree that the structures found within the diseased cells are 

 organisms at all, much less the causes of the troubles. Unfortunately, 

 cultivation of such organisms upon artificial media, and in pure cul- 

 tures, has never succeeded. Indeed, up to the present time no one 

 has succeeded in cultivating a cell-infesting rhizopod, and Liihe goes 

 so far as to state that it will never be done, although success with forms 

 like the Leishman-Donovan bodies makes such sweeping generaliza- 

 tions unsafe. The only means of determining whether such things are 

 organisms rests upon morphological evidence, and lacking cultural 

 possibilities the only proof that they are the cause of disease is to find 

 them in every case of the disease. The morphological evidence, to 

 most pathologists, is insufficient, and to most of them these organisms 

 are more probably artefacts or degeneration products of the human 

 cells caused by the disease, than etiological factors. To a proto- 

 zoologist, however, the morphological evidence of organic structures 

 of these protozoa is far more convincing, for he is familiar with the 

 many variations in size and structure, in the different phases of the 

 life history, of hundreds of different kinds of protozoa, and the struc- 

 tures seen in these questionable inclusions become to him convincing 



