28 OEIENTAL PLAGUE chap. 



sink to the bottom of the fluid. This falling of copious 

 flakes of growth from the surface to the bottom is graphi- 

 cally compared by Haffkine to a fall of snowflakes. On 

 further incubation new stalactites are developed, which 

 in their turn, on shaking the culture, become detached, 

 and fall to the bottom to increase the deposit. In this 

 way — by rest and then shaking — in the course of four to 

 six weeks a continuous re-formation of bacillary masses 

 (stalactites) can be ensured, so that by this time consider- 

 able amounts of bacillary sediment are obtained. A flask 

 of slightly alkaline ghee broth infected with B. pestis, 

 and kept for some weeks at 25° C, shows an almost com- 

 plete pellicle of growth on the top of the fluid, and from 

 it projects downwards into the fluid a dense forest of 

 threads or stalactites, which on slight disturbance rapidly 

 fall to the bottom (Figs. 44 and 45). 



The formation of stalactites in ghee broth kept in a 

 perfectly quiet place is very characteristic for B. pestis ; 

 but it has to be added that unless the culture is kept in a 

 place where absence of all disturbance, vibration, etc., can 

 be ensured, no visible stalactites are formed. I have 

 shown that a strain of B. pestis after many transferences 

 in artificial culture may lose the power to form stalactites 

 altogether, but regains this power when passed through an 

 animal. B. pestis obtained from a case of pneumonic 

 plague in 1896, and kept up in the laboratory in sub- 

 culture, failed completely to form stalactites in ghee broth 

 in 1899, but at once regained this power when cultures 

 were again started from the spleen and bubo of a guinea- 

 pig dead of acute plague after subcutaneous injection with 

 this same strain. For diagnostic purposes the formation 

 of stalactites in ghee broth is of value, although in practice 



