14 



correspondingly greatly increased. And it is precisely 

 materials which contain such mixtures (water, milk, shellfish 

 fouled by filth and excremental matters) that we are often 

 called upon to analyse for the presence of the B. typhosus. 

 In ordinary domestic sewage the number of B. coli com- 

 munis alone amounts to between 100,000 and one million, 

 or even more, per 1 c.c. ; in ordinary normal fcecal matter 

 B. coli communis alone amounts to something between 

 40 or 50 millions and 400 to 1000 millions per one gram, 

 in the fluid typhoid stool (pea soup stool) the number of 

 B. coli amounts to something like 14 to 20 millions per 

 1 c.c. The B. coli communis, as also other coli-like microbes 

 belonging to the coli-typhoid group, grow in all the media 

 in which the B. typhosus is capable of growing, and unfor- 

 tunately with greater ease and rapidity; but there is no 

 medium known in which the reverse is the case, and it will 

 therefore be readily understood that by cultivation the only 

 method which as the first step in the analysis can be resorted 

 to the isolation of the B. typhosus from amongst a number 

 generally an overwhelming number of coli-bacteria and 

 other microbes in a given mixture must be, in the nature of 

 things, an extremely difficult matter, unless the B. typhosus 

 should happen to be present in very large numbers. Add to 

 this the well-recognised fact that, taking the above tests 

 for differentiation of the B. typhosus from the other species 

 of the coli-typhoid group, the differences are small, and some 

 of them more or less those of degree only, and a negative 

 result qua isolation of the B. typhosus from the polluted 

 materials can be easily understood, although the polluted 

 material (water, shellfish, milk) had been proved to be speci- 

 fically polluted with typhoid excreta, having produced typhoid 

 fever in the consumers. 



Under these circumstances, any method by which 

 even the favouring growth and the rapid recognition by 

 culture of bacteria belonging to the coli-typhoid group 

 could be effected is of advantage, though it is only a 

 first small step; this is achieved by Parietti's method 

 (adding a certain amount, 05 per cent., of phenol to the 



