PROOF OF MOSQUITO ROLE 197 
lowed the developmental stages of the parasite to the end, thus verifying the dis- 
coveries of Ross. He had in June of the same year, without knowledge of Mac- 
Callum’s investigation, detected the process of fertilization and the function of 
the flagella as spermatozoa. 
In the course of his malarial investigations in Java, late in 1899, Koch dis- 
covered that when malaria is endemic it is often confined almost entirely to the 
children, a fact which he had already noted previously in East Africa; the adults, 
therefore, that have survived have acquired a certain degree of immunity. 
Koch found that very little malaria was in evidence in localities which seemed 
to be favorable in every way. He therefore sought a native village, which was 
situated in the midst of swamps and offered optimum malarial conditions, for 
the purpose of making blood examinations of the natives. He found that the 
adults did not suffer from malaria while a large percentage of the children did, 
the youngest ones being worst infected. Koch’s discovery of the frequent in- 
fection of naked children in the tropics, Ross considers to be one of the highest 
importance. It indicates the possibility of the disappearance of the effects of 
malaria, and that such apparently immune individuals, harboring the malarial 
parasites, are the source of most malarial infections in the tropics. 
Large scale practical demonstrations were soon made. One of the most in- 
teresting was that carried on in Italy by Professor Grassi during the summer of 
1900 in the Plain of Cappacio near Salerno. The objects of this experiment 
were: (1) To afford an absolute proof of the fact that malaria is transmitted 
exclusively by the bite of mosquitoes; (2) To formulate, in accordance with 
the results, a code of rules to be adopted to free Italy from malaria within a 
few years. The experiment consisted in protecting from mosquitoes rail- 
way employés and their families along about 12 kilometers of railway in an 
intensely malarious region. These people lived in ten cottages and two stations 
at St. Nicolo, Varco, and Albanella, situated along the Battipaglia-Reggio Rail- 
way. They numbered 104 persons, including thirty-three children under ten 
years of age. Of these 104 individuals, at least eleven, including four children, 
had never suffered from the disease, not having previously lived in a malarious 
district ; a certain number, it appeared, had not suffered from it in two or three 
years, and all the others, that is to say, the large majority, had suffered from it 
during the previous malarial season, some of them even in the winter. During 
the malarial season, the health of the protected individuals was exceptionally 
good ; there were a few cases of bronchitis and one of acute gastro-enteritis, and 
none of these cases were treated with quinine. Among these 104 persons, only 
three cases of malaria appeared and these were clearly relapses from malaria 
acquired the previous year. The unprotected neighbors, however, without excep- 
tion, contracted malaria. 
Another very striking experiment which, during the autumn of 1900, was 
mentioned in newspapers all over the world, was that performed by Doctors 
Sambon and Low, of the London School of Tropical Medicine, in the Roman 
Campagna, reputed for its malaria, during more than three months of the late 
summer and early autumn of 1900. They had constructed a comfortable little 
