372 GLANDERS ANTHRAX PYOCYANEUS 



the same manner to serve as controls. Incubation is continued at 

 37 C. for seventy-two hours, because the reaction is usually slow in 

 developing. Sterility must be maintained throughout. Strongly 

 positive sera may give a definite clumping in twenty-four hours or 

 less; the supernatant fluid becomes clear, and the organisms , collect 

 as a diffuse sediment at the bottom of the tube. A negative reaction 

 is indicated by a turbid supernatant fluid. The reaction may be 

 made microscopically or macroscopically, the latter being preferable. 



Attempts have been made to shorten the reaction time by aiding 

 sedimentation with the centrifuge. The various dilutions are incu- 

 bated for a full hour at 37 C., allowing fifteen minutes for the tubes 

 to reach 37 C. in the incubator; then they are whirled for fifteen 

 minutes at a speed with a twenty-four inch radius not exceeding 15dO 

 revolutions, placed in the ice-box and examined after three hours. 

 The slowly developing reactions may not be definitely positive for 

 twenty-four hours. 



A reaction in a dilution of 1 to 500 (horse, ass or mule) is the lowest 

 limit to which a definite reaction may be attributed, and the result 

 should be controlled w T ith a mallein test. Dilutions of 1 to 750 or 

 higher are usually safely regarded as diagnostic. In human cases a 

 positive reaction in a dilution of 1 to 100 is diagnostic. 



The method of complement fixation (see page 164 for details) is 

 rapidly becoming a general method for the diagnosis of glanders. 



Dissemination and Prophylaxis. Glanders is transmitted by direct 

 contact, by infection through cutaneous abrasions and cuts, and by 

 feeding paraphernalia, watering troughs and buckets. In man cuta- 

 neous infection is more common. 



BACILLUS ANTHRACIS. 



Bacillus anthracis was first seen by Davaine 1 in 1863, in the blood 

 of animals infected with anthrax. Koch 2 confirmed Davaine's obser- 

 vation, obtained the organism in pure culture, and reproduced the 

 disease with these cultures in other animals, thus establishing the 

 etiology of anthrax. He also demonstrated spore formation by B. 

 anthracis upon artificial media. 



Morphology. Bacillus anthracis is a rod-shaped organism measur- 

 ing from 1 to 1.50 microns in diameter and from 2 to 4 microns in 



1 Compt. rend. Acad. Sci., 1863, Ivii. 



2 Cohn's Beitr. z. Biol. der Pflanzen, 1876, ii, 277. 



