APRIL 5, 1901.] 
ours. But while we may properly let the 
recollection of the storm and stress of this 
earlier period fade away, the moral of the 
conflict should be held up as a permanent 
warning to scientific as well as unscientific 
‘men; for no episode in the previous experi- 
ence of the race demonstrates so clearly the 
sources of knowledge and the methods of 
attaining it. 
As a final illustration of the validity of 
my thesis I would invite your attention to 
one of the most instructive and beneficent 
of the many brilliant biological researches 
of recent times. No one who has suffered 
from repeated attacks of intermittent fever, 
and has survived the ravages of the ma- 
teria medica, can fail to take a lively inter- 
est in the wonderful progress made during 
the last twenty years towards a definite 
knowledge of the natural history of that 
disease. Nor can any one interested in the 
general aspects of science fail to see in the 
investigations leading up to this progress 
some of the finest examples of the scientific 
method. 
It would appear that malarial fever has 
been one of the commonest disorders, in 
certain localities, with which man in his 
struggle for existence has had to cope; and 
before the discovery of the properties of 
Peruvian bark it must have been a very 
serious affliction by reason of its secondary 
if not by reason of its primary effects. The 
symptoms, course and distinguishing char- 
acteristics of the disease, as well as the 
remedies therefor, were long known, how- 
ever, before it was suspected that the mos- 
quito had anything to do with its dissemina- 
tion. Bad water, foul air, and sudden or 
extreme changes of temperature were sup- 
posed to be promoting causes. The damp- 
ness of marshes, swamps and other areas 
holding stagnant water was held to be an 
especially common attendant, if not induc- 
ing, condition. There was, indeed, no lack 
SCIENCE. 
529 
of acute and painstaking observations and 
no lack of ingenious and well-supported 
hypotheses with regard to this widely prev- 
alent but obscure disorder. The details of 
its diagnosis, prognosis, nature and cansa- 
tion, as laid down in the medical manuals 
of a few decades ago, are particularly inter- 
esting and instructive reading now in view 
of recent developments. For example, 
Hartshorne in his ‘ Essentials of the Prin- 
ciples and Practice of Medicine,’ published 
in 1871, gives the following explanations : 
““ No disease has ordinarily so regular a 
succession of definite stages as intermittent 
fever, namely, the cold, the hot, and the 
sweating stage.” * * * ‘¢ Upon the origin of 
malarial fevers,’’ he adds, ‘‘ the following 
facts seem to be established: 1. They are 
reasonably designated as autumnal fevers, 
because very much the largest number of 
cases occur in the fall of the year. Spring 
has the next greatest number of cases. 2. 
They are always strictly localized in preva- 
lence. 8. They never prevail in the thickly 
built portions of cities. 4. Anaverage sum- 
mer heat of at least 60° F. for two months 
is necessary for their development. Their 
violence and mortality are greatest, how- 
ever, in tropical and subtropical climates. 
5. They prevail least where the surface of 
the earth is rocky; and most near marshes, 
shallow lakes and slow streams. The vi- 
cinity of the sea is free from them, unless 
marshes lie near it. 6. The draining of 
dams or ponds, and the first culture of new 
soil, often originates them. 7. Their local 
prevalence in the autumn is always checked 
by a decided frost.”’ 
Here we have the facts with regard to the 
symptoms and cause of the disease stated 
with a clearness and a conciseness that 
could hardly be surpassed. But the real 
cause of the malady eluded the insight of 
the discriminating observers who collected 
those facts. A quite different class of facts 
required consideration. It was essential 
