250 ORIENTAL PLAGUE chap. 



readily detached and falls to the bottom of the fluid, 

 only to be in the course of a few days replaced by 

 a similar fresh scum. In this way, viz. by keeping the 

 flasks for the last two to three weeks at the temperature 

 of 25° C. and shaking the flasks every three or four days, 

 the greatest amount of sediment (granules and flocculi of 

 growth) will be obtained. It is a fact, although it does 

 not well agree with a general assumption, that not even 

 after four weeks is the growth finished, i.e. is the 

 nutritive material in broth exhausted. This may appear 

 strange, since in the case of a rapidly growing microbe 

 like the B. pestis one would a priori expect that at 

 a temperature of 37° C. the growth would have been 

 completed and the broth " exhausted " in the space 

 of ten days or a fortnight. But this is manifestly not 

 the case ; after a fortnight's incubation at 37° C. the 

 flasks, on transference to a temperature of 25° C, 

 exhibit a conspicuous further growth, which continues 

 even to the end of six weeks. In regard of all flasks so 

 treated, subcultures were made on gelatine and agar with 

 a platinum loop, a single loopful being transferred from 

 the flask to the new culture medium. In every instance 

 great numbers of colonies developed, particularly in the 

 gelatine tubes. This proves that the bacilli in the flasks 

 were still living and active ; that they had not, as was 

 to be anticipated, died off in the course of a few weeks 

 in large numbers. I think, with Haffkine, that the 

 addition of the clarified butter is the important means 

 by which the bacillary growth is maintained and its 

 amount increased. 



In the course of the last two years I have sealed 

 and sterilised nearly 12,000 tubes (each containing 



