[May, 
264 The Ghost of the Season. 
Switzerland which soaked through an entire mountain of 
oolitic rocks, yet on emerging into another valley was found 
to have brought with it the infection of typhoid fever. 
The present writer has seen flocks of sewage fungus along 
with the effluent from a large, fairly deep, and well managed 
sewage irrigation farm. Surely, then, it may be contended 
that the main ground for the alleged superiority of sewage- 
irrigation to precipitation processes is substantially aban- 
doned by the above-quoted admissions of Dr. Percy 
Frankland. He, indeed, argues that if filtration cannot 
remove disease-germs, so a fortiori cannot precipitation — a 
mistaken inference. There is, in the first place, no evidence 
that the proportion of organic matter in water bears any 
constant ratio to the number of disease-germs which it may 
contain. . 
If we accept to the full the germ theory we must admit 
that if the dejedta of a single cholera or typhoid fever patient 
be thrown into a pure mountain stream, the effedt upon the 
health of a community lower down will be more serious than 
if the sewage of an entire village had been poured into it. 
Hence determinations of organic nitrogen and organic car- 
bon, and “ previous sewage contamination,” throw sur- 
prisingly little light upon the safety or danger of using a 
stream as a domestic water-supply. 
But there are fadts which prove that precipitation pro- 
cesses — all those at least which employ aluminous salts as 
precipitants — are not less, but more effectual, guarantees 
against the presence of disease-germs than any filtration or 
irrigation process. 
For centuries it has been customary in China to add to 
suspicious and polluted waters a pinch of alum, strain off 
the clear liquid after standing for some little time, and use 
it for drinking or cooking. For some years the French 
troops in Cochin China suffered severely from dysentery of a 
very malignant kind. It was observed at last that if this 
Chinese expedient was used persons drinking the water es- 
caped the disease. The microbia are not necessarily killed, 
but are precipitated and remain in the sediment. 
So decisive is this reaction that Dr. Brautlecht has intro- 
duced it as a means of detecting badteria, &c., in waters. 
He makes a solution of sulphate of alumina, acidulates it 
with hydrochloric acid, and adds a few drops of this liquid 
to the water he is about to examine. A few minutes after- 
wards he adds cautiously a few drops of ammonia, so as. to 
neutralise the whole. A precipitate is formed which carries 
down with it the badteria. It is filtered off, re-dissolved in 
