THE WATER-SUPPLY OF TOWNS IN THE TKOPICS 293 



equally resistant to such forces of nature as the action of sunliglit and t)ie action of 

 storage. Otherwise, if it can be proved that one organism is particularly resistant, and 

 another particularly susceptible to these natural forces, it is obvious that the resistant 

 organisms cannot be considered, on all occasions, of equal value, as an index of recent 

 and dangerous pollution, as the susceptible ones. Examining the ten organisms, which fall 

 under Houston's definition of 'coli,' and which represent his worst type of pollution, we 

 are prepared to state from actual experiments, that the greatest possible variation Vavying 

 exists in these ten organisms in their power of resistance to the action of natural forces, po^^f^ °' 



... . resistance to 



To take two extreme examples B. (/nuiHiul is particularly resistant to the action of the sunlight 

 sunlight. It is found in waters that have been exposed to the tropical sun for weeks ; it amongst 

 is nearly always one of the last bacilli to disappear from a well-sunned and stored water, organisms 

 and also from a mixture of cow-dung and water exposed to the sun. On the other hand, 

 true B. coU communis of Escherich (the organism that ferments dulcit and does not ferment 

 saccharose, adonit, inulin, etc.), will disappear with great rapidity from a water exposed 

 to the action of the tropical sun. It is seldom found to survive longer than three days in 

 a clear water of considerable depth. Is it reasonable to include both these bacilli under 

 the same term of ' true coli,' and to state that both equally represent objectionable 

 pollution ? It is possible to elaborate this still further. In the course of our work we 

 have found that under very exceptional circumstances, a bacillus known as Oxijlocuti 

 perniciosns is occasionally found in a water-supply. There is good reason to believe that 

 this organism is extremely susceptible to natural conditions, such as sunlight, etc., for 

 although it is present in cow-dung, and probably in human ftEces, it has only been found 

 in water-supplies after heavy floods, and it disappears with extraordinary rapidity. 

 Thus, it is probable that this organism represents a more recent, and therefore a more 

 objectionable contamination, tlian any other organism met with up to now. Yet it will 

 be observed that this j^articular bacillus does not fall within Houston's definition of ' true 

 coli,' nor within the category of organisms which, according to Savage, are ' equally of 

 excretal origin.' " 



Such being the case, why, asks Clemesha, do the methods employed in England yield, 

 as they undoubtedly do, such satisfactory results ? He answers this as follows ; — 



" Firstly, the majority of the contamination in surface and river waters is due to Ciemesha's 

 human excrement in the form of sewage from towns. '■""'■ "^'°"^ 



"Secondly, the guiding principles that assist a water analyst in arriving at a conclusion, 

 are based on the study of organisms present in sewage, that are human in origin. Thus, 

 the reason Houston gives for saying that saccharose fermenters do not represent so 

 objectionable a form of pollution as the non-saccharose fermenters, is, because the non- 

 saccharose fermenters greatly preponderate in sewage. It should be noted that this kind 

 of reasoning would obviously lead us into serious error in India, where nuich of our 

 pollution is due to animals. 



" Thirdly, there is very little doubt that coli communis of Escherich (dulcit -t- , saccharose, 

 adonit, inulin, Voges and Proskauer — ) is probably the commonest organism found in 

 human fteces, and in rivers polluted with town sewage. The work of MacConkey supports 

 this view. 



"Fourthly, B. coli communis of Escherich is a very susceptible organism to the forces 

 of nature that are inimical to bacilli generally, and its presence therefore does actually 

 represent a recent and dangerous contamination. Evidence in support of this statement 

 can be found in Houston's annual reports, where the ratio between his ' true coli,' 

 ' confirmatory ' and ' presumptive ' tests, varies with the time of the year. Thus, in 



