PROOF OF MOSQUITO ROLE 197 



lowed the developmental stages of the parasite to the end, thus verifying the dis- 

 coveries of Eoss. 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, Eoss 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 \vith 

 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 employes 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-Eeggio Eail- 

 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 Eoman 

 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 



