52 BACTERIA IN WATER 



beings. They are present in human faeces and in crude sewage in 

 considerable number; and as we have said, they are absent from 

 relatively large amounts of pvire waters and virgin soils, but present 

 in abundance in water and soil recently polluted with animal 

 dejecta. It is not claimed that all streptococci are necessarily delicate 

 germs, or pathogenic, or of recent animal outcome. ' It may be that 

 certain streptococci are comparatively hardy germs, and that others 

 may be capable of multiplying in Nature outside the animal body. 

 Again, there may be streptococci in Nature which do not owe their 

 origin to excremental matter, and doubtless many of them may be 

 non-pathogenic, although this latter circumstance is no proof that 

 at a stage prior to their isolation they were non-virulent, nor does 

 it impair the value of the test as an indication of recent fouling with 

 objectionable matters. 



Houston found streptococci habitually present in crude sewage 

 in iTjVij- c.c, present in human faeces in one milligramme, and present 

 in minimal quantities of soils and water recently polluted with 

 matters of animal outcome. These results encourage the belief that 

 the streptococcus test is one of the most delicate yet suggested for 

 detecting recent, and therefore, presumably, specially dangerous, 

 pollution. 



The question of relative abundance in connection with the strepto- 

 coccus test also deserves consideration. For if streptococci are absent 

 from 10 c.c. or more of pure waters and present in xinnr c.c. of 

 crude sewage the distinctions as regards streptococci between water 

 and sewage is sufficiently great to allow of considerable latitude being 

 observed in framing a standard without seriously impairing the value 

 of the test. What standard should be adopted is a matter of opinion, 

 but as a rule it may be said that the presence of streptococci are to 

 be thought of as indicating extremely recent, and B. coli less recent, 

 but still not remote, pollution of animal sort (Houston). The 

 presence of B. enteritidis sporogenes, however, cannot be considered to 

 afford evidence of pollution -bearing a necessary relation to the recent 

 evacuations of animals. Streptococci and B. coli are either altogether 

 absent or present in sparse amount in virgin soils, and may be 

 absent even from polluted soils, unless the contamination is of 

 comparatively recent sort. In soils recently polluted with animal 

 matters streptococci and B. coli are of course present in abundance. 

 B. enteritidis sporogenes may be present even in seemingly virgin soils, 

 but in sparse proportion compared with the large number found in 

 cultivated and polluted soils. Lastly, the presence of streptococci 

 in any number in a water supply points not only to recent animal 

 pollution, but also implies that the antecedent conditions — condi- 

 tions intervening between the period of pollution of the water and the 

 time of collection of the sample — could hardly have been of so un- 



