The Examination of Waters. 7 



ware, will separate the minute bacteria forms from the Yan 

 Yean, but the beautiful, bright filtered water obtained from 

 this filter contains their germs. Some good scientific 

 observers claim to have made filters which will separate 

 germs ; but it is possible, I think, that they have been 

 experimenting on water in which the bacteria were exhausted 

 or dying, and in which there were no germs ; for after they 

 (the bacteria) have brought about the chemical changes of 

 which they are capable they do die out ; and it has been a 

 point of interest to watch how each of the waters under 

 examination passed through its various stages, and one form 

 replaced another till all died. Whether we ever reach a 

 stage in which there are no germs present I am not certain, 

 but think that it is probable, and that in the rapid 

 changes the disease germs may suffer in the same way as 

 harmless bacteria. Bacteria are so easily killed, and it is so 

 easy to destroy, or perhaps I should say prevent, their 

 germs from developing that we may hope for some means 

 for in a like manner destroying disease germs, and I think 

 some simple salt may do this. 



But, as Mr. Balfour Brown says, for proof in connection 

 with this subject " we must be content to wait for the 

 fuller revelation, which may be reached through long bills 

 of mortality in time to come ;" and quoting from Dr. Cayley's 

 Croonian lectures, " I think these two instances (the 

 Gatherum and Lausen cases) are sufficient of themselves to 

 serve as a warning against trusting to irrigation and down- 

 ward filtration as a means of purifying water, and also 

 against the dictum that water containing less than a certain 

 proportion of organic impurity is practically wholesome and 

 fit for drinking irrespective of its original source. It ought, 

 I think, to be laid down as a rule of hygiene that human 

 excrements should under no circumstances be mixed with 

 drinking water, however completely they may be subse- 

 quently removed by filtration or rendered innocuous by 

 oxidation. Of course, in the case of London this can only 

 be looked upon as an ideal to be realised in some distant 

 future ; but with less than this we ought not to rest satisfied." 

 " Living matter," says Dr. Alfred Hill, '"' does not get oxidised 

 by flowing down a stream any more than a fish. It is not 

 decomposing animal matter which is prejudicial, but actual 

 living matter. Mere dilution by water does not deprive it of 

 its dangerous qualities." Dr. Frankland says : " I do not 

 think it possible by any practical means that have been 



