300 THE PATHOGENIC RHIZOPODA 



of the intestine which they are incapable of reaching by their own 

 movement. On the other hand, the nearly pure cultures of the ameba 

 which Strong, Musgrave and Clegg, and others have succeeded in 

 raising and in causing the disease in normal animals, and Schaudinn's 

 experiments on kittens with dried spores of E. histolytica, speak for 

 their specific pathogenic nature. Musgrave and Clegg ('04), indeed, 

 are so positive of the pernicious effect that they maintain the patho- 

 genic nature of all intestinal amebse, and claim that ordinary pond or 

 soil dwelling amebse may become pathogenic on entering the intestine. 

 Taking all into consideration, there is no doubt that the intestinal 

 rhizopods are dangerous, and are either the causes of certain types 

 of the disease, or pernicious accessories of the cause. 



If skepticism exists as to the pathogenic nature of entameba and the 

 causes of dysentery in general, what can be said as to neuroryctes and 

 cytoryctes and the causes of hydrophobia and smallpox? With 

 entameba, skepticism never reaches the level of denial of the organism, 

 but with these other organisms not only does doubt exist as to their 

 connection with disease, but their claims to relationship with living 

 forms are widely denied. The problems are certainly very difficult, 

 and with the immense numbers of degenerations, secretions, and the 

 like which may be imagined in tissues under diseased conditions, it is 

 easily possible to be mistaken when morphology is the sole criterion. 

 But it is not inconceivable that these difficulties are overestimated, 

 and that the questionable structures in diseased tissues are actual 

 organisms. 



Certainly no one doubts that rabies and smallpox are germ diseases, 

 and it is equally certain that no other cause, apart from these cell 

 inclusions, is known. There is a strong a priori reason, therefore, for 

 believing that these intracellular structures in cells which are known 

 to be the seat of the disease are the actual causes and not the product 

 of the diseases. Thus, the Negri bodies (Neuroryctes hydrophohioB) 

 are constant inclusions in the brain cells of victims of rabies, and the 

 Guarnieri bodies (Cytoryctes variolas) are equally constant inclusions 

 in the skin cells of man and apes infected with smallpox. So strong 

 is the morphological evidence of the nature of these inclusions that 

 there is no doubt whatsoever in my own mind as to their protozoan 

 nature and to their affinities with entameba and other rhizopods. 



The transition from the intercellular to these intracellular para- 

 sites of the rhizopod type is shown by such unquestionable ameboid 

 forms as Plasmodiophora brassicce, while recently a number of other 

 forms of similar nature have been described. Among these the 

 genus which Prandtl ('07) describes under the name of allogromia is 

 very instructive. This is a parasite of free-living protozoa, such as 

 Ameba proteus, arcella, nuclearia, or even paramecium, unicellular 

 hosts which become infected with the sexual generation of the alio- 



