MEANS OF DEFENCE AGAINST MICROBES. 249 
in the intestines is always due to the use of unfiltered 
water, and this should enforce the general use of 
filters, which is often neglected even by those who 
cannot be deterred by the relatively moderate cost 
of an instrument which it is almost impossible to 
wear out. An ordinary filter, however, can arrest a 
very small proportion of microbes, which are much 
more minute than the ova of ascarides. 
A filter has, therefore, been devised, so perfect as 
to allow the passage of no solid matter in suspension, 
not even the most minute organisms contained in 
drinking-water. This result is effected by the filter 
invented by Chamberland in Pasteur’s laboratory. 
The filter is formed (Fig. 101) of a vessel of biscuit- 
ware, A, shaped like a candle (whence its name of 
bougie Chamberland); this is fastened to the lower 
part of the metallic receiver D, which receives under 
pressure the water coming from the cock E. This 
vessel consequently filters the water from without to 
within, and it flows through the orifice B, perfectly 
free from solid particles, as it appears from a micro- 
graphic examination. 
Fitted to the distributing water-taps of many 
houses in Paris, and especially in lycées, the Cham- 
berland filter acts under the normal pressure of the 
water-conduit, and, by a new modification of the 
inventor, can even act without such pressure. For 
this purpose he arranges his filters in a battery, from 
eight to ten or more, in a cylindrical receiver, closed 
12 
