DESCRIPTIONS OF PATHOGENIC BACTERIA. l6l 



tain. In gelatin tube culture the growth along 

 the line of inoculation takes the form of a 

 brush, while single colonies appear almost like 

 bone cells ; the bacteria do not grow upon 

 potato, and upon agar they do not grow so 

 characteristically as in gelatin. They retain 

 the stain when treated by Gram's method. In 

 swine they evoke a simple cutaneous erysip- 

 elas which makes its appearance in the form 

 of large patches ; they may pass over second- 

 arily into the blood, in the cells of which they 

 are frequently enclosed (Fig. 256), although 

 they occur also in the free condition. Rabbits 

 in like manner develop erysipelas at the place 

 of infection and from that starting-point sub- 

 sequently develop septicaemia. House mice 

 and especially white mice are extremely sus- 

 ceptible, and sicken at the outset with septi- 

 caemia. The mouse is found after death sitting 

 in a characteristic position with its back curved. 

 Blooded swine are more susceptible than ordi- 

 nary swine, while cattle, sheep, horses, car- 

 nivorous animals, guinea-pigs and especially 

 field and wood mice are completely resistant. 

 Virulent cultures become less virulent in their 

 passage through rabbits, more virulent in their 

 passage through pigeons. Natural infection 

 of swine may* take place by means of the food ; 

 the bacilli pass out of the body with the excre- 



