In many cases the physical conditions of the soil have undergone
no appreciable change during centuries, so that it is impossible to
attribute so enormous an augmentation of malaria to an increase in its
annual production, itself increased by a progressive alteration of the
chemical composition of the soil. But if, on the contrary, it be admitted
that malaria is caused by a living organism whose successive generations
accumulate in the soil, the interpretation of this fact becomes very
simple.
There are, finally, _peculiarities in the local charging of the atmosphere
with malaria_ which can be explained only in this manner. If the malarial
miasm were composed of gaseous bodies emanating from the soil, or rather
of chemical ferments formed beneath the ground and raised into the air by
gases or watery vapor, the charging of the atmosphere with the specific
poison ought to arrive at its maximum during the hottest part of the day,
when the ground is heated the most by the sun's rays, and when the
evaporation of water and all chemical actions attain their maximum
intensity. But this is very different from what actually occurs. The local
charging of the atmosphere is always less strong during the meridian hours
than at the beginning and the end of the day, that is to say, after the
rising, and especially after the setting, of the sun.
Pages:
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171