61 



EXPEEIMENT IX. 



This experiment was undertaken to test the behaviour of 

 oysters towards the B. coli communis of ordinary domestic 

 sewage. One dozen " small Dutch oysters " were obtained 

 from a first-class shop in the City the oysters had just 

 arrived direct from Holland. The oysters were carefully 

 brushed under the tap and placed in a clean tank in 2000 c.c. 

 of sterile sea water. Twenty-four hours after, two were taken 

 out for analysis by Drigalski plates two plates for each 

 oyster. The result was that neither of them contained in 

 -j^ and part of the body of the fish any B. coli communis 

 that is to say, in none of the four plates were any red 

 colonies with red halo to be found. 



The test by Drigalski plates, as I have already explained, 

 is undoubtedly the best that we have, and for this reason : 

 that only B. coli communis produces on these plates already 

 after 24 hours at 37 C. round distinctly red colonies, 

 several millimetres in breadth with red halo ; and if no such 

 colonies, viz., largish red with red halo, make their appear- 

 ance in 48 hours, according to my experience extending 

 now over a considerable number of analyses the conclusion 

 is justified, and is confirmed by other culture tests, that no 

 B. coli communis is present in the material analysed. I 

 must insist on this, for the reason that all other methods 

 used for preliminary diagnosis are decidedly inferior, because 

 colonies of the above kind invariably respond to all tests 

 of B. coli communis, whereas the colonies of other microbic 

 species, unlike the above red colonies with red halo, on the 

 complete series of tests being made do not answer to 

 the true B. coli communis. Although in several of the tests 

 they may simulate the B. coli, if the tests are completed, they 

 can be proved to be not the true B. coli communis, but to 

 be different from this, the typical and constant microbe of ex- 

 cremental matters. I have for years past now more than 

 12 years insisted on a distinction being drawn between 

 the typical B. coli communis of excremental matters and 

 what, owing to one or the other similar character, may be 



