BACTERIOLOGICAL EXAMINATION OF WATER 447 



distribution of streams of sewage in bodies of water into which they 

 flow, their disappearance by dilution and sedimentation, and their 

 removal by death. Under peculiar conditions bacteria in water may 

 increase for a time, but here the prevailing bacteria belong almost 

 exclusively to one type. 



Streptococci in Sewage. The varieties of streptococci found most 

 often in polluted water correspond to the streptococci described by 

 Houston. In some water in which these are found no B. coli have 

 been found and there is considerable doubt in such cases as to whether 

 the streptococci imply serious pollution. The streptococci remain 

 alive much longer than the colon bacilli, and therefore, probably, than 

 the typhoid bacillus. 



The Proteus Group. Members of the proteus group are often found 

 in polluted waters and but rarely in pure water. The bacillus pyo- 

 cyaneus is also at times present, and has in a few cases excited infectious 

 diarrhoea. Bacillus cloacae is a common form of sewage bacteria. 



Isolation of the Typhoid Bacillus from Water. If it were possible 

 to readily obtain the typhoid bacilli from water, when they were present 

 in small numbers, its examination for that purpose would be of much 

 greater value than it is now; but we have to remember that we can 

 only examine at one time a few cubic centimetres of water by bacterio- 

 logical methods, and that although the typhoid bacilli may be sufficiently 

 abundant in the water to give, in the quantity that we ordinarily drink, 

 a few bacilli, yet it must be a very lucky chance if they happen to be 

 in the small amount which we examine. Still, further, although it is 

 very easy to isolate typhoid bacilli from water when they are in con- 

 siderable numbers, yet when they are a very minute proportion of all 

 the bacteria present it is almost impossible not to overlook them. Many 

 attempts have been made to devise some method by which the relative 

 number of the typhoid and other parasitic bacteria present in water 

 could be increased at the expense of the saprophytic bacteria. Thus 

 to 100 c.c. of water 25 c.c. of a 4 per cent, peptone nutrient bouillon is 

 added, and the whole put in the incubator at 37 C. for twenty-four 

 hours. From this, plate cultures are made. In our experience this 

 and other methods, such as collecting the bacteria left on a filter after 

 passing several gallons through, have not enabled us to detect the 

 typhoid bacillus where we have failed to find it by making direct plate 

 cultures. As a matter of fact, the typhoid bacillus is rarely found, 

 even in specimens of water where we actually know that it is or has 

 been present because of cases of typhoid fever which have developed 

 from drinking the water. From these facts we must consider our lack 

 of finding the bacillus in any given case as absolutely no reason for 

 considering the water to be free from danger. Another serious draw- 

 back to the value of the examinations for the typhoid bacillus is that 

 they are frequently made at a time when the water is really free from 

 contamination, though both earlier and later the bacillus was present. 

 It is hardly worth while, therefore, except in careful experimental 

 researches, to examine the water for the typhoid bacillus, but rather 



