ANTHRAX 135 



Branell in the blood of a man in 1857. Davaine worked 

 with this organism from 1863-73 ; Koch in 1876 succeeded 

 in growing it outside the living body and establishing 

 its pathogenicity. 



The anthrax bacillus is the largest of all pathogenic 

 bacteria ; in length it varies from 5 to 6 m, in breadth 

 from 1 to 1"5 fi. It is aerobic, although not strictly so, 

 for it will grow without the presence of free oxygen, viz., 

 in the blood of animals and in ' stab ' cultures. It is not 

 motile, is usually straight, and has square ends, which are 

 very characteristic. In the blood, where it occurs singly 

 or in short chains, the ends of the bacillus are very slightly 

 convex, and when stained sometimes show a central longi- 

 tudinal mark more deeply stained than the rest of the 

 protoplasm. In wool-sorter's disease the organism occurs 

 in the fluid of the lungs in long threads, generally without 

 any appearance of segmentation. 



When growing, the bacillus elongates, and then gradu- 

 ally divides transversely in the middle, the two bacilli thus 

 formed being enclosed in a common sheath. Under favour- 

 able conditions this process may continue until chains of 

 great length have been formed. When the bacilli have a 

 good supply of oxygen, and the temperature is between 

 24° or 26° C, spores are developed. In sporulation the 

 protoplasm first becomes granular, and clear spaces occur, 

 which soon take a definite oval shape and become highly 

 refractive. The substance of the bacilli will then gradually 

 break down and dissolve, leaving the spores free. When- 

 ever a free spore finds itself in a suitable medium for its 

 development, it elongates and loses its high refractivity, and 

 the protoplasm bursts through the membranous wall and 

 escapes as a bacillus. 



When spores develop in a chain of bacilli, they do so at 

 fairly regular intervals. These chains of bright spores 



