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It may be well to discuss the value of some of these tests 
in a little greater detail :— 
(rt) The total Colonies on Agar.—This should always 
form part of the examination. It affords very valuable 
information regarding the bacilli, other than the lactose fer- 
menters, that are present in a given sample. By comparing 
the total colonies with the number of lactose fermenters pre- 
sent in the bile salt broth the relation between fecal and 
ordinary water organisms is roughly ascertained. The partic- 
ular value of the total counts is not so much in comparing 
samples from different parts of a Province, though this 1s 
possible, but in comparing the various samples derived from 
the same source. Here it may be pointed out that as a routine 
method we usually take 4 or 5 samples from each system ; 
one from the natural water, whether it be well, spring or river ; 
one taken immediately after filtration (whether it be filtered 
through a gallery or through constructed filter beds) ; and 2 or 
3 samples from the distributary system, and the service res- 
ervoir if there be one. We not infrequently find that the 
number of lactose fermenting organisms in a system varies 
very little wherever the samples are taken, but the total 
colonies in I c.c. gives us much valuable information as to the 
efficiency or otherwise of the filtration, the action of the pipes 
on the water, and the presence or absence of silt in the terminal 
branches of distributary system. One is perfectly prepared 
to admit that gelatine as a culture medium is superior to agar 
for this work, because besides giving all the information agar 
does, it differentiates between the liquefiers and the non-lique- 
fiers of gelatine; further the colonies of the various bacilli 
present certain characteristic appearances on this medium, 
Neither of these advantages can be claimed for agar-agar ; but 
the difficulties in the way of working with gelatine are so great 
in hot climates, that they seriously interfere with its usefulness. 
(2) Vosges and Proskauer Reaction.—The Vosges and 
Proskauer reaction has been the subject of very considerable 
controversy. Some regard this test as being very variable, 
at one time giving the reaction, and at another failing to give 
it with the same bacillus. Orrin his work on milk says: “‘ The 
reaction has been given by other organisms than lactis ero- 
