76 MICRO-ORGANISMS AND DISEASE [chap. 



wells ; if there be no soakage of sewage, practically no 

 bacillus coli will be found in it, but if there be such soakage 

 bacillus coli is easily found in moderate numbers. It must 

 be obvious that where sewage pollution does take place, the 

 facility of discovering the bacillus coli in the water will 

 depend cieferis paribus on the relative amount of pollu- 

 tion and water. If, for instance, it is a case of a small 

 water-course to which sewage has continually access, num- 

 bers of colonies of bacillus coli would be found in a gelatine 

 plate made with even small quantities of the water, say 

 \ — I or 2 cc. But if it is a question of a water-course like 

 the river Thames, even after a moderate sewage pollution, the 

 volume of water is so great that bacillus coli can be demon- 

 strated only by subjecting large quantities of the water to the 

 culture test. To expect to find the bacillus coli in a few 

 drops or even a few cc. of water taken from the Thames at 

 Hampton, above the intake of the water companies' water, 

 is very strange, and stranger still to say that not finding it 

 in so small a quantity, it is absent from the unfiltered 

 Thames water at Hampton ; such statements are liable to 

 throw doubt on bacteriological examinations in the eyes 

 of sanitarians, for it is notorious that apart from the surface 

 flushing of streets in many places on the upper Thames, 

 there is obvious pollution of the Thames with human excre- 

 ments, along the shore, from barges, house-boats, &c. And 

 the same applies to the examination of water for typhoid 

 bacillus or cholera vibrio — viz., it is essential that large 

 volumes of water should be subjected to bacterioscopic 

 examination, and even then a negative result should be put 

 forward for what it is worth. Statements such as one 

 occasionally sees — viz., a few drops or a few cc. of the water 

 had been examined and no bacillus coli, or no bacillus of 

 typhoid, or no cholera vibrio was found, therefore such 



