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Employed without care and attention, a mosquito net is little protection in such malariou places as nost up-country African stations.
2. Subsidiary measures. — In many of the more malarious places we visited we con- sidered that other subsidiary precautions, such as will suggest themselves to any intelligent person, were also necessary. To protect our legs and ankles, for instance, we considered it necessary to wear thick trousers, with puttees, or the very convenient so-called mosquito boots. The face and hauds are not in waking hours very likely to be bitten by Anopheles, though they are very likely to be bitten by various species of culex, It must be understood, however, that for precautions to be effective in badly malarious places considerable care and thoughftulness is entailed, and few followed our example.
3. Quinine.-During the whole of our three years' life in the tropics we found it quite uncessary to use quinine. If, however, the bites of Anopheles cannot be guarded against quinine should be taken as a prohylactic. We consider Professor Koch's method of taking 15 grains on two successive days in each week as the best. Repeated small doses are of doubtful efficacy.
II-BLACKWATER FEVER.
Considering the fatality of this disease, and the fear it inspires in the European in Africa, we fully realised the importance of trying to solve the vexed question of its cause.
We believe that facts observed by us based on direct microscopical evidence have placed on an absolutely satisfactory footing its malarial nature. The importance of this has a great added value because it follows that the prophylaxis is identical with that of malaria, and the European who can protect himself from attacks of malaria will have no fear of contracting blackwater fever.
It has been held by the majority of competent observers in recent years in the tropics, notably A. and F. Plehn and Ziemann, that blackwater fever was malarial in nature. The most important objection to this view is that a microscopical examination of the blood in blackwater cases is generally negative, ie., shows no malarial parasites, or so few as to make it doubtful if they could be associated with the attack. This then was practically the state of our knowledge when we commenced our work on this fever.
In
our investigations into the ordinary forms of malaria, however, in the tropics, we soon recognised that in severe malaria also an examination of the blood might, in certain cases, reveal no parasites, or in other cases very few, quite insufficient, apparently, to account for the severe symptoms. Such cases were those in which quinine had previously been taken, so that it was not an uncommon experience for a blood examin- ation to show, before the taking of quinine, numerous parasites, whereas later, while still high fever and severe symptoms continued, parasites might be entirely absent. Nor was it exclusively in cases where quinine had previously been taken that parasites were absent. In certain cases, though we believe these are comparatively rare, parasites may be absent, or if present, are so few in number that they bear no proportion to the severity of the attack. And, indeed, our experience has been confirmed by others working both in the tropics and in Europe by Celli. Ziemann. Schaudin.* Thus the last named says, in case I., parasites were present during the attack and during the intervals of the fever, but in case II. they were almost always absent on the day after the attack and during the attack they were very scanty, although the fever was extraordinarily severe.
We were led then, in such cases as these, to seek for other proofs of the malarial origin of the fever. Two such methods were adopted by us: the first consisted in a thorough search in extensive blood films for pigmented leucocytes, which are evidence of a recent attack of malaria. The second was by a determination of the relative proportion of the different varieties of leucocytes in the blood. We followed out this line of observation at length and found that in malaria a relative increase of the large mononuclear leucocytes took place, and were led to consider a value as high as 20 per cent. as evidence of an antecedent malarial attack. Similar observations had also
* Arbeiten, a d. k. Gesundheitsamie, s. 234, Bd. xix.