556 BACTERIOLOGY. 



A single attack of symptomatic anthrax, if not fatal, 

 affords subsequent protection ; while infection with the 

 malignant oedema bacillus appears to predispose to re- 

 currence of the disease. (Baumgarten.) 



BACTERIUM WELCHII, MIGULA, 1900. 

 Synonym : Bacillus aerogenes capsulatus, Welch and Nuttall, 1892. 



This organism consists of straight or slightly curved 

 rods with rounded ends, somewhat thicker than bacte- 

 rium anthracis, varying in length ranging from 3 to 6 

 microns ; sometimes longer chains or threads are seen. 

 The rods are surrounded by a transparent capsule, 

 whether grown in artificial media or obtained from 

 animal bodies. It is a non-motile, spore-forming 

 organism, and is strictly anaerobic in character. It 

 stains with the ordinary aniline dyes and by the Gram 

 method. 



Under anaerobic conditions the organism grows on 

 the usual culture media at room temperature, and forms 

 large quantities of gas in media containing carbohy- 

 drates. Gelatin is not liquefied. In agar-agar the col- 

 onies are usually from 1 to 2 millimetres in diameter, 

 but may be as large as 1 centimetre in diameter. They 

 have a grayish-white color, are flat, round or irregular 

 masses, with small hair-like projections from the mar- 

 gin. In bouillon there is a diffuse clouding and marked 

 white sediment. Milk is quickly coagulated. On 

 potato there is a grayish-white layer. 



The organism grows more rapidly at 30 to 37 C. 

 than at 18 to 20 C. Cultures on agar-agar and bouil- 

 lon have a slight odor resembling old lime. Bouillon 

 cultures are killed after ten minutes at 58 C. 



Bacterium Welchii was first described by Welch in 



