Page:Popular Science Monthly Volume 69.djvu/415

Rh Schaudinn regards Entamœba coli as a harmless commensal, but Entamœba histolytica as a definite tissue-destroying parasite, a faculty which gives to this form of tropical dysentery its pernicious and often fatal characteristic.

From dysentery to hydrophobia seems a long jump and yet we may find that these two diseases and with them others apparently as diverse, as small-pox, sleeping sickness, etc., owe their malignancy to the destructive action of protozoa on different tissues of the body. I take up rabies next because the organism of hydrophobia agrees in many of its characteristics with that of dysentery, and belongs, as I believe, on the present evidence, in the group of rhizopods.

Peculiar structures have been known for several years in the brain and nerve cells of animals with rabies. Negri, however, in 1904 was the first to suggest that these are as distinctive of hydrophobia as Plasmodium is of malaria, and he and his assistants succeeded in establishing the conviction that these 'Negri' bodies are sufficiently characteristic to afford a quick and safe diagnosis of rabies. Beyond the suggestion that these bodies are organisms comparable to the smallpox organism as described by Councilman and his collaborators, Negri did not attempt to outline their systematic position. From the apparent absence of nuclei and other structures in the Negri bodies, pathologists have been inclined to interpret them as secretions, or degenerations of a specific type, and very few have been hardy enough to regard them as protozoa. Among these few, however, is Dr. Anna W. Williams, of New York, who spent a summer at Woods Hole three years ago, working on protozoa, and who has done a great deal on pathogenic protozoa; and to her belongs the credit of establishing the protozoon nature of these enigmatical structures.

One of the curious features of pathogenic protozoa is that they are very refractory to the ordinary cytological stains, and do not behave like other cells under hematoxylin or methylin blue, etc. This is why the organism of syphilis was overlooked until last year, and this is why Negri failed to get any evidence of cell structure in his rabies organism. In all of his preparations and figures the bodies appear as highly vacuolated structures with no sign of nucleus or differentiated cell body. Dr. Williams, using the Giemsa stain, a method that has been singularly successful in staining delicate pathogenic protozoa, showed that not only do these Negri bodies have a definite structure with nucleus and cytoplasm, but also that a series of nuclear metamorphoses occur which are identical in their consecutive phases with the typical freeliving rhizopods. Nuclear fragmentation takes place until as in Entamœba or Centropyxis or Amœba, etc., the cell is filled with