BIOLOGICAL STUDY OP TAP WATER. 419 



eases are produced directly by these forms, it is quite proper that 

 we should be very careful that the water we drink is free from them 

 if possible. If we look for natural water however which is absolutely 

 free from Bacteria, probably we shall look in vain. But we must 

 remember chat all forms of Bacteria are not capable of producing 

 disease, even if some are, or at any rate that they do not do so under 

 ordinary circumstances, but only in particular and well-marked con- 

 ditions of the organism or organ attacked by them. We must not 

 be surprised then to find Bacteria in our water supply. I have 

 observed even in fresh filterings all the common forms, micrococci, 

 rod-like forms, vibrios, spiral forms, and zooglaea stages. But if the 

 filterings be allowed to stand exposed to the air for a few hours, it is 

 amazing how rapidly they increase in numbers, and after a day or 

 two the whole becomes converted into one mass of Bacteria in all 

 stages, growing at the expense of the other oi-ganisms, and eventually 

 leaving nothing but the siliceous frustules of Diatoms, and whatever 

 other matter like this defies their digestive power. Probably there 

 is no place where they thrive better, and where they exist in greater 

 numbers, than in the School of Practical Science ; for they are 

 .certain to be found there in everything which is not positively 

 ^destructive to them. There is no doubt then that their presence in 

 such abundance in sediment which has been allowed to stand for 

 ?some time exposed may be in great measure accounted for by germs 

 .getting into it from the atmosphere, as well as those already there 

 multiplying. 



Adopting the view held by Billroth, Nageli, Cienkowski, Ray 

 Lankester, and Zopf, that all the forms usually described under the 

 generic names Micrococcus, Bacterium, Bacillus, Leptothrix, Clado- 

 thrix, Vibrio, Spirillum, Spirochaete, &c, are only development 

 stages of Schizophytes, in opposition to that of Cohn and others, 

 that they are distinct species without morphogenetic connection, all 

 the forms observed have been referred to the two species, Gladothrix 

 dichotoma, Cohn, and Beggiatoa alba, Vauch. 



Concerning the first of these two Zopf remarks, that " what the 

 common bread mould (Penicillimn crustaceum) is among the aerial 

 mould fungi, G. dichotoma is among the aquatic fungi, and therefore 

 it might be quite properly denominated the 'water-fungus' (' Was- 

 serpilz') par excellence." 



