HUMAN DISEASES 527 



been successful, particularly where it has been possible to intro- 

 duce a piped water-supply. Freetown, for instance, which used 

 to be a hot-bed of yellow fever, has had very few cases since the 

 introduction of a piped water-supply more than twelve years ago. 



Again in the Belgian Congo, at the ports on the lower river, 

 especially Matadi, a special department in charge of water-sup- 

 plies and anti-mosquito work was established after the last epi- 

 demic of yellow fever in 1927-8, with the result that Aedes and 

 yellow fever now rarely occur. Other measures, such as the British 

 plan of separating the European from the native quarters of towns, 

 have had their effect. But there have been some calamities also, 

 notably the yellow fever epidemic in Bathurst in 1 934, when four 

 Europeans, including the Colonial Secretary, died from the disease. 

 In this outbreak it was manifest that the infective zone was in the 

 European residential area, and subsequent investigations by Dr. 

 Findlay showed that the reported cases were only a fraction of those 

 which must have occurred. 



Preventive vaccination against yellow fever was introduced in 

 America by Sawyer and his collaborators. Two methods of vacci- 

 nation are now being applied extensively, that of Sawyer, Kitchen, 

 and Lloyd (1931) with modification by Pettit and Stefanopoulo 

 (1933), and that of Laigret (1934). Dr. Findlay (1935) of the Well- 

 come Research Institute in London, who was sent to New York 

 by the Colonial Office to study the Sawyer technique, has vacci- 

 nated by the first method more than 900 persons proceeding to 

 West Africa. In French Senegal, Dr. Laigret has vaccinated more 

 than 3,000 Europeans by the second method, using vaccine pre- 

 pared from mouse brains at the Pasteur Institute in Dakar. The 

 results from either method are not always satisfactory, since the 

 reactions of individuals to yellow fever differ so markedly, but 

 yellow fever vaccination has undoubtedly produced results which 

 warrant its extended use among Europeans. 



SLEEPING SICKNESS 



The severe epidemic of sleeping sickness in the four years 1901- 

 1905, when some 300,000 people died of the disease in the imme- 

 diate neighbourhood of the Victoria Nyanza, has stimulated 

 much research and many experiments in control, but knowledge 



