230 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
our absolute freedom from malaria. Employed without care and attention, a 
mosquito net is little protection in such malarious places as most up-country African 
stations. 
2. Subsidiary measures. — In many of the more malarious places we visited 
we considered that other subsidiary precautions, such as will suggest themselves to 
any intelligent person, were also necessary. To protect our legs and ankles, tor 
instance, we considered it necessary to wear thick trousers, with puttees, or the very 
convenient so-called mosquito boots. The face and hands 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 thoughtfulness is entailed, 
and tew followed our example. 
3. Quinine. During the whole of our three years' life in the tropics we 
found it quite unnecessary to use quinine. If, however, the bites of Anopheles 
cannot be guarded aeainst, quinine should be taken as a prophylactic. We consider 
Professor Koch's method of taking fifteen grains on two successive days in each 
week as the best. Repeated small doses are of doubtful efficacy. 
II. BLACK WATER FEVER 
Considering the fatality of this disease, and the fear it inspires in the European 
in Africa, we fully realized 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 exami- 
nation of the blood in blackwater cases is generally negative, i.e., 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 recognized 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 examination to show, before the taking of quinine, numerous parasites, whereas 
