SEA-FISHERIES LABORATORY. 153 
of all those studied are glucose +, lactose +, indole +, 
V. and P. —, immotile forms. The method of analysis 
certainly enables one to describe the majority of the bacteria 
isolated as belonging to fairly well-marked categories, each 
of which is distinguished by a set of similar characters, the 
number of which is, to some extent, a compromise. 
The next step towards making bacteriological analyses 
afford definite results is to associate each of these categories 
with some combination of physical characters. We may 
suppose that “ typical” B. colt communis, and other organisms, 
exist in large numbers in the human alimentary canal and 
reproduce there, preserving their characters. But before 
entering the shell cavities and alimentary canals of mussels 
they traverse drains, sewers and sea-water, so that their 
further multiplication occurs in various environmental con- 
ditions. Probably they are highly mutable, and since a large 
number of successive generations may appear in a relatively 
short time there is opportunity for selection, and so for the 
production of new strains in a comparatively short time. 
If the period elapsing between the voiding of typical B. coli 
communis, or other truly faecal organisms, and the infection 
of shell-fish were a very short one, we might expect to recognise 
these organisms in the latter habitat in relatively large numbers, 
but if this period is prolonged we ought to find the descendants 
of mutants of the original strain. We ought to be able to 
conclude, from identification of the prevalent “species” of 
bacteria found in the shell-fish, what were the environmental 
histories of the infecting organisms; whether the latter had 
had their origin in the human intestine, or in some other 
source, uncontaminated by faeces, and what was the probable 
duration of the period after leaving the human and entering 
the molluscan alimentary canal. This recognition of the 
relative significance of the various kinds of bacteria that may 
be found in polluted mussels or sea-water is the really important 
