HUMAN DISEASES 539 



This work has special medical interest, since rats and their fleas 

 are probably responsible for spreading at least two tropical dis- 

 eases in addition to plague, namely Weil's disease and typhus 

 fever. Of the latter, two cases have recently been diagnosed 

 authoritatively in Freetown, probably its first official occurrence 

 in West Africa. 



The flea factor in the spread of plague is a subject which 

 requires investigation. There is evidence to show that the rat-flea 

 population is different in town and country, and this may explain 

 what seems to be low infectivity in certain outbreaks. Dr. Hopkins, 

 Medical Entomologist in Uganda, has published (Symes and 

 Hopkins 1932) preliminary notes on this question. 



With regard to preventive and control measures, anti-rat cam- 

 paigns are carried out in nearly all infected centres, and sometimes 

 have proved successful in small local outbreaks, but they are useful 

 only where every building can be cleared completely. This calls 

 for complete supervision of the type that can be applied in towns, 

 but not in rural areas. The typical native thatched hut provides 

 a favourable home for rats and their fleas, so improved housing 

 in areas of dense population is a primary consideration. The use 

 of poison gas, especially cyano-gas, in native huts has proved 

 effective, and can usually be relied on to kill 75 per cent of the 

 rats; it has the great advantage over the old method of removing 

 the thatch of huts in that it is far less unpopular. Its introduction 

 has therefore led to more complete notification of plague cases. 

 Rat-proofing of granaries and food stores is another important 

 measure; an extensive anti-rat campaign along these lines 

 proved very successful in Kenya in 1936 (Kenya 1936, D.R.). 

 Motor-buses give every facility for host distribution. Plague, there- 

 fore, like so many other diseases, will succumb eventually only to 

 all-round improvement in hygiene. 



Prophylactic vaccination has been made compulsory in some 

 parts of Africa and research on it has been conducted especially 

 by Dr. J. H. Harvey Pirie at the South African Institute for 

 Medical Research. There is still some difference of opinion as to 

 whether vaccines should be made from living or dead cultures. 

 At the Pan-African Conference of 1935 it was concluded that 

 detailed methods of plague control cannot be standardized, especi- 



