HUMAN DISEASES 525 



assigned three members of its yellow fever staff to Uganda, to 

 occupy the Human Trypanosomiasis Laboratory at Entebbe, 

 recently vacated by Dr. Duke {see page 485). It is important to 

 recognize that the mouse protection test does not prove the pre- 

 sence of the virus, but only indicates that the individual has at 

 some time had yellow fever, which may subsequently have died 

 out from the area. It serves to define the extent and concentration 

 of immunity in various age-groups of a population, but gives no 

 indication of the state of affairs at the moment. Hence the finding 

 of actual cases is important. 



Intensive research is being conducted for actual clinical cases of 

 yellow fever in the silent areas where the mouse protection test 

 indicates the existence of the virus, but from which, up to the 

 present, the disease itself has not been recorded. One of the enigmas 

 of yellow fever arises from the fact that during epidemics many 

 people are infected and become immune without apparently show- 

 mg clinical symptoms. Therefore, attempts are being made, not- 

 ably in the Anglo-Egyptian Sudan, to isolate the virus from sus- 

 picious cases in order that its characters may be fully studied. 

 Apart from detection of the virus, the existence of the disease may 

 be proved by microscopical post mortem examination of the liver, 

 and for this purpose a special technique has been applied with 

 marked success in South America. A special instrument, the vis- 

 cerotome (Morgan 1935) enables the layman to remove specimens 

 for dispatch to pathological laboratories without the necessity of 

 handling the corpse or tissues, and with the minimum mutilation 

 of the body. In South America the viscerotome service has proved 

 the existence of yellow fever in many places, and enables action 

 to be taken to prevent emanation of the virus from known infected 

 points. It has shown, moreover, that the silent areas are silent, 

 not because fatal cases do not occur, but because symptoms are 

 not typical. The information can be obtained by the viscerotome 

 without posting trained medical staff in every locality where the 

 disease is suspected. A viscerotome service has been inaugurated 

 in the larger centres of population in the Gold Coast (League of 

 Nations 1936, p. 76), and in West Africa it is hoped that valuable 

 data may be obtained and the services be extended. The chief 

 difficulties are (i) the objection of Moslems to interfering with 



