620 SEDGWICK AND WINSLOW. ■ — BACILLUS OF TYPHOID FEVER. 
they require nearly twice as long for their develo2)ment as do the normal germs and 
these few and weakened germs very likely could not produce many, if any, cases of 
typhoid fever, for vitality and virulence in disease germs are probably closely related. 
AVitli art! fie 
different, for such ice is made from 
frozen solid, and is, as a rule, quickly consumed. Artificial ice, if made from pure 
water, should be above reproach ; but if it be made from water that is impure it 
may contain the germs of infectious disease ; and inasmuch as artificial ice is used 
quickly after its manufacture, the possibility of purification by time is excluded, and 
such ice might therefore conceivably be a menace to the public health. 
With natural ice, as long as absolute sterilization is not effected, there must always 
remain a certain element of doubt, as in the use of sand filters, alluded to above, or in 
the practice of room-disinfection after 
o 
The thickness of a lay 
of ice is oRen artificially increased by cutting holes in it and flooding that already 
formed with the water of the pond. In such a case the effects of crystallization are 
laboratory tubes. Ice thus formed might be cut at once, and 
onal case we cannot say that 
led 
served within a week or two ; and in such an except 
sufficient of the virus might not persist to excite the malady. Yet such an instance 
must be very exceptional; and the general result of human experience, the absence 
of epidemics of typhoid fever traced conclusively to ice, the fact that cities like 
New York, and Lowell and Lawrence in Massachusetts, have used the ice of polluted 
streams, and have yet maintained low death-rates from typhoid fever, all tend to 
support the conclusion at which we have arrived, namely, that natural ice can very 
rarely be a vehicle of typhoid fever. 
