I 
4 
SEDGWICK AND WINSLOW. — BACILLUS OF Tyi«Il..iD FEVm. 
6in 
IV. DEDUCTIONS FROM THE EXPERIMENTS CONCEIiNIXG ICE AS A VVUWhE 01 
INFECTIOUS DISEASE, WITH SrECIAL KEFEKENCE TO THE riI'>l;LEMS 
OF ICE-SUPPLY AND THE PUI^LIC HEALTH. 
Reviewing the several series of experiments described in detail above and k 
I 
ing carefully in mind the conditions under which natural ice i« fornud, ciil,l.ai\('^l(»d 
stored, delivered, and finally consumed, as well as those pertnining to tlio inanufac 
ture, distribution, and consumption of artificial ice, certain conchisions appear <o h( 
justified concerning ice as a vehicle of disease; and these conclusions me, on iIh 
whole, decidedly reassuring. 
f 
The conditions which tend naturally to purify polluted waters, arc now well 
stood. Light, cold and poor food-supply are antiseptic or diMnfectant agenh ( 
siderable power; hostile infusoria may devour the living germs of infeciiotiH disca^-; 
the chemical composition of the water may be unfiivorable to their survival; and 
gravity may cause them to settle to the bottom, where they may soon perish for wajit 
of air. The main factor determining the reduction of germs in water is, however, the 
time, — the time during which these and other forces are left to act. EpidemioloL'-y 
shows clearly that disease follows best a direct, quick transfer of infections mnferial 
from patient to susceptible victim ; and, if storage of water for some months could 
be insured, many sanitarians would consider such storage a sufficient purification. 
In ice we have this condition realized, — a forced storage of at least weeks and at 
best of many months. At the same time the other effective conditions arc also 
heightened. It is no w^onder, then, that our experiments show a reduction of over 
99 per cent in typhoid bacilli frozen; and Ave may be sure that in nature tlie 
destruction would exceed, rather than fall short of, such a limit. 
This reduction obtains in tubes which are frozen solid, where there is no chance 
for mechanical exclusion. In natural ice there is another purifying influence. Of 
the germs remkinino- in the water at the time of freezing, 90 per cent are thrown out 
the physical phenomena of that process. This reduction is separate from, and 
supplementary to, the disinfecting action of the cold. Accordingly, when both 
factors work together, it is obvious that only one out of a thousand typhoid germs 
present in a polluted stream has a chance of surviving in the ice. 
Under natural conditions the pathogenic germs present in the most highly pol- 
paratively few. Of these few, one-tenth of one per cent may 
uted 
^e present in ice derived therefrom. But even 
ttercd Individ 
akened by their soiourn under unfavorable conditions^ so that, as wc h 
ir sojourn 
