222 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
the only difference being that it is not conveyed by contact, but only by the Anopheles 
mosquito. 
Malaria then is an infectious disease — the infection or malaria parasite being 
conveyed from one person to another by the bite of Anopheles. An Anopheles 
mosquito, per se, is harmless ; it is only an Anopheles containing parasites, or, in other 
words, an infected Anopheles, that can transmit malaria, and the only way by which 
an Anopheles can become infected is by ' biting ' some person who has the parasite in 
his or her blood. 
It at first sight seems strange that the infective character of malaria has been 
and is still so overlooked by the general public. The actual mode of infection, how- 
ever, has lately been made clear. Malaria is not in the tropics usually contracted 
from ' fever ' cases, but almost always from ' latent ' malaria in the native population. 
Native Malaria 
1. Koch, in the East Indies, almost everywhere found malaria in the 
children, though adults were free from infection. He commonly found malarial 
infection only on microscopical examination of the blood. In some of the villages 
examined by him every child had malaria, in others a smaller proportion. He came 
to the conclusion that the degree of infection he found in these children was a test of 
the intensity of malaria. 
2. We, ourselves, finding that Anopheles caught in native villages always 
contained a considerable percentage of infected specimens, were led to the discovery 
that this was dependent upon a general infection of the native children of Africa 
who, although apparently in good health, had almost always the malarial parasite in 
their blood. We were thus able to show that the home of malaria is in native huts, 
hamlets, villages, and towns, and that European malaria is a mere resulting sign of 
the vast degree of indigenous latent malaria. 
This has been amply confirmed subsequently by other observers, notably by 
Annett and Dutton in Nigeria, Ziemann in the Cameroons, and again by ourselves 
in India. 
The Infection of Anopheles 
Where human infection is so general we should also expect to find Anopheles' 
infected, and, indeed, in any batch of Anopheles caught in native huts a greater or less 
proportion always contain sporozoits, i.e., the malarial parasite in a condition ready 
for infecting man. The number of Anopheles infected is a variable one. As a rule 
in Africa it is from five per cent, to ten per cent., but reached in some villages fifty 
per cent. Aro, on the Lagos railway, was an instance where the sporozoit rate in 
Anopheles caught in native huts was fifty per cent. Obviously it would be as difficult 
to avoid malaria in such a place as smallpox in a smallpox hospital 
