1885.] 
Recent Researches on Malaria. 
663 
_ As regards the influence of temperature, it may be men- 
tioned that for the most part malaria does not occur beyond 
63° N. latitude and 57 0 S. latitude; from these limits it in- 
creases towards the Equator, with a gradual increase both 
in intensity and extent. 
|_If we consider that in the Southern Hemisphere there 
are mere desolate islands, such as South Shetland at 57° 
latitude, we shall not lay great weight upon the southern 
limit above given. But according to many authorities ma- 
laria is much less general than in the Northern at such 
latitudes as 40", and even 30 0 .] 
Here the question is not so much the mean annual as the 
mean summer temperature. If, in a region where malaria 
is generally frequent, the mean summer temperature is ex- 
ceptionally low, e.g., below 68° F., the malarial forms occur 
slightly or not at all. If the temperature rises they become 
more intense. 
[It must here be remembered that up to the earlier part 
of the last century malaria was regularly present in Lin- 
colnshire and other parts of the eastern coast of England, 
though a mean summer temperature of 68° F. is certainly 
very exceptional.] J 
The second factor necessary for the development of ma- 
laria in the soil is the access of air to the malariferous strata 
of the soil. If in low grounds there often occur inunda- 
tions which carry with them and deposit much earth, there 
is formed by degrees an accumulation of soil which, if thick 
and dense enough, cuts off the access of the air to the sub- 
soil, and thus stops the development of malaria. This is a 
form of sanitation which often takes place without human 
aid [but which is sometimes imitated by man. “ Warping,” 
as it is called, is proposed as a means for the sanitation’of 
the malarial low grounds near Rome] . 
If, inversely, such old buried malarial foci are laid bare 
and turned up in the course of engineering or agricultural 
operations, the fevers reappear. Hence we may conclude 
that the malarial germ requires for its development the 
access of atmospheric air ; it is an aerobic organism. 
With the importance of the access of air to the malarious 
subsoil the existence of moisture is closely connected. The 
occurrence of malaria in relatively dry, elevated regions, 
teaches us that a very moderate degree of moisture ^suffi- 
cient for the production of malaria. 
[Here then comes a difficulty : how can we drain the 
subsoils sufficiently without letting in the air ?] 
It for a long time no rain has fallen, so that the soil loses 
