77 



from that sewage the non-liquefying vibrio and the motile 

 B. streptoides, both forming blue colonies but of different 

 aspect, size, and constitution, and therefore capable of being 

 at once recognised by means of the Drigalski plates. In the 

 analysis of oysters for sewage microbes the presence in 

 Drigalski plates of these two species may therefore be of 

 diagnostic value. 



We append here a number of photographic representa- 

 tions of the appearances in Drigalski plates made with 

 typhoid materials ; although the colonies are not coloured in 

 these photograms, it is not difficult to recognise their 

 character. 



These photograms are reduced to half the actual size ; all 

 colonies, except when specially mentioned, appeared blue, 

 and of the uniform character and aspect of the typhoid 

 colonies, as described in the text; there was no difficulty 

 when inspecting them under a glass of ascertaining their 

 nature, which was also confirmed by agglutination test and sub- 

 cultures in the various media made of various colonies 

 indiscriminately chosen. 



SERIES I. 



Fig. 1. Plate charged with T OO<JO~ part of a cubic centi- 

 metre of sea water immediately after infection of the sterile 

 water with culture of B. typhosus (see Experiment IV). 

 This plate contained 247 colonies of B. typhosus and no 

 others ; this amounts to 2,470,000 B. typhosus per 1 c.c. 



Fig. 2. Same sea water, 75000 P ar ^ f a cu bi centi- 

 metre 24 hours after infection ; the plate contains 153 

 colonies of B. typhosus ; in addition one large (opaque) and 

 one small (dot-like) colony not blue and not B. typhosus; 

 this would therefore amount to 1,530,000 B. typhosus per 

 1 c.c. 



Fig. 3. The sea water in which the infected oysters had 

 been kept had been changed 24 hours previously ; T L c.c. of 

 it now examined yielded 1318 blue colonies of B. typhosus, 



