SEDGWICK AND WINSLOW. — BACILLUS OF TYPHOID KE\TR. 571 
stant, so striking, and so universal. The parallelism between tlie nn'ves of (yplioid 
and of temperature is too close not to suggest in the strongest maimer Muiie din'(;l 
relation such as was postulated by Murchison, Liebermeister, and Davidson. No one 
doubts a direct correlation between the growth in a wlieat-field and the clianges of 
temperature during the changing seasons. The fundamental properties of protoplasm 
are so constant that there seems no reason to doubt a similar favorable effect of tlie 
warmth of summer, not on the crop of typhoid plants growing in human bodies, 1)iit 
r 
on the survival seed which passes from one body to another througli the enviroiuncnt. 
This is theoretical ; but the experiments reported in the first section of tliis p;iper 
furnish practical evidence to confirm the a priori hypothesis that it must b^ mnrc 
difficult for an organism habituated to a temperature of 98° ¥. to persist in Nature 
when the thermometer is at 30° than when it is in the neighborhood of SO^ 
We do not wish to assert that the typhoid bacillus multiplies in the environment 
during the summer months of a temperate climate. It is the absence of the destruc- 
tive influence of cold, rather than any stimulating influence of heat, which permits the 
rise culminating in the autumnal maximum. 
In fine, the probable mechanism of the seasonal changes according to our conception 
(r is as follows : — 
The bacteriology and the jBtiology of typhoid fever both indicate that its causal 
agents cannot be abundant in the environment during the colder season of tli.' year. 
The germs of the disease are carried over the winter in the bodies of a few patients 
and perhaps in vaults or other deposits of organic matter where they arc protected 
from the severity of the season. The number of persons who receive infection from the 
discharge of these winter cases will depend, other things being equal, upon the length 
of time for which the bacteria cast in these discharges into the environment, remain 
alive and virulent. The length of the period during which the microbes live wil 
depend largely upon the general temperature; as the season grows nnlder, more and 
more of each crop of germs sent at random into the outer world wdl survive long 
^ ^ The process wdl be cumu- 
Ji to gain entry to a human being and bear fruit. Hie pr 
lative. Each case will cause more secondary cases ; and each of 
a still more extensive opportunity for widespread damage. In oi 
, • .• r.f tvnl.nid fever is a direct ellect 
reasonable explanation of the seasonal variations ot t>piu)ia ^^^^^ 
temperature upon the persistence in Nature of germs which procee r 
victims of the disease. 
the most 
of 
