ii CHARACTERS OF THE B. PESTIS 27 



drop of fluid under the microscope can the actual presence 

 of growth be ascertained. 



In neutral-red beef broth the growth is of the same 

 character as in ordinary alkaline broth (see below), the 

 normal cherry colour of the neutral-red broth remaining 

 unaltered. 



B. pestis does not thrive in glucose taurocholate 

 peptone water (MacConkey fluid), nor in lactose peptone 

 water, nor in peptone salt water. 



B. pestis grows well at 37° C. in faintly alkaline beef- 

 broth peptone ; the broth remains clear, but along the 

 glass wall and at the bottom there appear whitish granules 

 and flocculi, these being masses of the bacilli, many 

 forming longer or shorter chains ; 1 as growth proceeds 

 the amount of floccular sediment increases, but is not at 

 any time very copious. Pakes and Joseph (Transactions 

 of the Pathological Society of London, vol. lvi. p. 135) 

 show that B. pestis grows in slightly acid broth, and by 

 this means can be readily differentiated from the pneumo- 

 coccus present in the sputum of pneumonic plague. 



For the production in broth of greater amounts of 

 bacillary masses, Haffkine hit upon the plan of covering 

 the top of the broth with a layer of clarified butter or ghee. 

 As mentioned above, when incubation takes place at a tem- 

 perature at which the ghee remains solid, i.e. temperatures 

 at or below 25° C, its (the ghee's) under surface becomes 

 covered with masses of growth hanging down like shorter 

 or longer whitish fringes (" stalactites ") ; these, on dis- 

 turbing the fluid, e.g. by shaking, become detached and 



1 The formation and the arrangement in chains is noticed in B. pestis whenever 

 it grows in fluid media — broth, fluid serum, condensation fluid of agar or serum and 

 the like. The same is observed in the peritoneal fluid. These chains at first sight 

 resemble streptococcus chains. 



