276 Proceedings of Royal Society of Edinburgh. [sess. 
wave of malarial fever passes over a district, the Tertian type is seen 
at its outbreak, whereas at the height of an epidemic, or whenever 
it assumes a severe character, the quotidian type obtains, and as the 
outbreak of sickness abates one meets with a return to the types of 
fever having a longer interval between the paroxsyms, so that in 
tropical and sub-tropical countries the fever takes on the Tertian type, 
and in the higher latitudes the quartan type makes its appearance. 
These remarks apply also to outbursts of the disease where it is 
endemic. In temperate zones remittent malarial fevers are exceed- 
ingly uncommon, in fact, so uncommon as to be regarded as a 
departure from the ordinary type and as due to exceptional causes. 
All races may suffer from malaria, although the Negroes are less 
prone to it, always provided that they do not migrate. Indeed, it 
is very generally acknowledged that in all parts of the world 
strangers suffer more severely from malaria than does the indi- 
genous population. The incidence of malaria is to a certain 
-extent governed by the seasons. In those places where it is 
endemic it occurs all the year round ; but where it is only 
slightly developed there are two maxima — one in spring and one 
in autumn, and a considerable decrease of the disease in the 
months between them. In regions with strongly developed 
malaria, there is a maximum beginning in summer, which reaches 
its height at the end of summer or the beginning of 
autumn, lasting not rarely into winter, and which so far exceeds 
the spring maximum, that the latter not unfrequently disappears 
altogether, so that there is only one minimum, winter and spring, and 
one maximum, summer and autumn. In tropical countries, in the 
worst malarious districts, the disease is most rife during the rains. 
The relation which malaria bears to heat is as follows — the greater 
the mean summer temperature, other things being of course taken 
into account, the more malaria, and the amount of malaria decreases 
with the mean annual temperature of the place, ceasing altogether 
with the summer isobar of 60° T. But, as Hirsch says, “ in higher 
latitudes, the malarial fevers which have prevailed endemically or 
epidemically in spring undergo for the most part a considerable re- 
mission on the setting in of summer heat, and they do not revive 
until the cooler weather of autumn,” and again, “in the regions of 
severe malaria the disease shows itself, and attains wide diffusion, 
