SELF IMPROVEMENT OF STREAMS 339 
3. Ice should have come from grossly polluted sources. 
4. It should be young ice—recently frozen. 
5. Cases should develop among ice-water drinkers chiefly. 
6. Ice should have been placed in and not around the water. 
Hill further states: “Ice, were it equally subject to contamination as 
water and without natural purification processes, could not, on account 
of its relative small use, constitute a factor accounting for over 2 of 1 
per cent of water-borne typhoid (which, of course, would be a much 
smaller proportion of the total typhoid of the country) even if its use 
were as gencral as the use of water.”’ 
Jordan (1911) states, ‘“‘ There has never been much danger from 
the use of impure ice; there need be none. Certified ice of a purity 
beyond reproach can be much more readily attained under existing 
conditions than pure water, and very much more readily than pure 
milk.” About the same opinion has been expressed by other sani- 
tarians. Bartow (1916) has stated, ‘‘ Nature certainly does her share 
toward a pure natural ice. If reasonable precautions are taken so 
that no ice is taken from grossly polluted ponds or rivers and the 
surface of the ice is protected, there need be no difficulty in placing a 
pure ice on the market.” 
Methods for the Bacterial Examination of Ice. After the ice has 
been sampled and the sample is melted, the methods of analysis, chem- 
ical and bacterial are no different than those used in water analysis. 
The sampling of the ice for the bacteriological analysis does, however, 
require some special attention. Care must be exercised to secure a 
sample which is not contaminated. This may be accomplished in dif- 
ferent ways. The block of ice should be carefully cleaned and washed 
with distilled water. Then, it should be copiously rinsed with sterile 
distilled water. After this it should be split if it is a large block and 
small pieces chipped off and transferred to sterile containers by means 
of sterile instruments. If this is carefully carried out no contamina- 
tion will result. The block may also be bored out with a sterile auger 
and the shavings collected in a sterile bottle. Greenfield (1916) has 
described an instrument for sampling ice. It is constructed after the 
cheese sampler. 
SeLF PURIFICATION OF STREAMS 
This is a subject which is becoming more and more important as 
population increases. It is very closely related to the disposal of 
sewage by dilution. Directly it may concern the viability of patho- 
