No. 7. DEPARTMENT OF AGRICULTURE. 189 



istics. They are oval or rounded in form and in size vary from ex- 

 ceedingly minute to the largest approailiing 25 microns in diameter 

 or length (see Plate IV). Those usually seen in the brain of the 

 dog of the street vary in size from barely visible forms to eight mi- 

 crons in diameter, rarely more. The smallest form are seen in rab- 

 bits dead from an injection of ''fixed virus," and most extraordinarily 

 large forms are seen in the cow dead of rabies. Negri bodies have 

 distinct staining affinities as they favor the basic stains over the acid^ 

 Within the body small, usually rounded but frequently irregularly 

 shaped inner bodies are seen that favor most all of the chromatin 

 stains, characteristic of nuclear material. With the stains now in 

 general use, these inner bodies take a blue to a black color, the in- 

 tensity varying with their size. The smaller the inner bodies, the 

 deeper the stain, while the rest of the body takes a light stain, a 

 purple to a pink, or various shades of red. The contrast is at once 

 striking, and these inner bodies encourage attention. The inner 

 bodies may be seen as a single body, which is true of those tiny 

 forms seen in the rabbit, and around these tiny forms, other granu- 

 lar material can be seen. The next larger forms show no appreciable 

 enlargement of the inner body. Usually in the Negri body showing 

 considerable granular material around the inner body, the inner body 

 is apt to be noticeably larger and not stained as deeply as the inner 

 body of the tiny forms. Then too, in the larger forms, not infrequently 

 several inner bodies are seen lying close to one another, but each 

 small arid deeply stained. Forms showing larger inner bodies not 

 so deeply stained are seen, and in addition several smaller deeper 

 stained inner bodies may either lie close to the larger inner body 

 or out in the structure around the inner body. Another form oi 

 much interest is the one in which the inner bodies are scattered! 

 through the Negri body, all fairly deeply stained. Not infrequently 

 a form in which these separate inner bodies stain rather deeply 

 scattered through the body, stand out prominently appearing to be 

 pushing out the outline of the Negri body, strongly suggesting pseu- 

 dopods or budding forms. Of the protozoa, the ameba or rhizapods 

 and sporozoa, exceedingly varied and complicated life cycles are 

 recognized. In one stage of the development of these protozos, ad- 

 ditional chromatin material makes its appearance within the cellu- 

 lar structure, either by a reduction of the chromatin of the nucleus 

 or by the elaboration of chromatin by the cytoplasm, the result of 

 some special stimulus affecting the nucleus or cell protoplasm. The 

 chromatin bodies are distributed through the cytoplasm, and these 

 chromidial forms form a distinct phase in the development of these 

 protozoa. The inner bodies of the Negri bodies, as chromatin or 

 nuclear material, occasionally show an arrangement or stage re- 

 sembling this chromidial stage of the rhizapods and aporozoa. The 

 I»osition taken by Williams and Lowden* in considering the Negri 

 bodies as protozoa and by Calkins^ that they are one of the ameba 

 or rhizapods is well founded, on the study of the various forms of 

 the bodies met with. The protozoon nature of the cause of rabies 

 receives additional support in that quinine will neutralize the virus 

 in test tubes. 



That Negri bodies are closely associated with the cause of rabies 

 has been proven by the uniformity with which it is possible to re- 



