1008 



FOOT-AND-MOUTH DISEASE. 



[Feb., 



Kent, it will be seen that 27 (about 43 per cent.) of the 63 initial 

 outbreaks in the last 20 years have appeared in this area. 

 Taking the Southern section of the country represented by 

 Hampshire, Dorset, Wiltshire, Somerset and Devon, 15 initial 

 outbreaks (24 per cent.) have arisen there. In both groups there 

 are areas, Cornwall and Middlesex for example, in which no such 

 outbreaks have occurred. There are also small areas, for 

 example a strip along the north coast of Wales in Carnarvon, 

 Flint and Denbigh, where they have arisen at least often enough 

 to be remarkable. 



It does not seem likely from what has been said that the inci- 

 dence of invasion in these areas can depend entirely on fortuitous 

 circumstances, and it is possible that if the explanation of this 

 incidence was forthcoming, it would also explain the method of 

 invasion in general. 



Air-borne Virus. — No support having been found for the 

 ordinary methods of conveyance of virus, it seems justifiable to 

 explore the possibility of the virus being air-borne for long 

 distances, either by air currents or birds, or otherwise. As 

 regards air currents, when affected cattle are allowed to remain 

 alive on open pastures or at work, as is customary on the Con- 

 tinent for example, it is no uncommon thing to see strings of 

 viscous slobber from the mouth whirled up into the air and 

 dispersed into minute parts which disappear from sight. This 

 material is known to be infective in infinitesimal doses, and it 

 can therefore stand a high dilution. What becomes of it after 

 it gets into the air is obviously a question which cannot be 

 answered definitely. It is a fact, however, that even in this 

 country where the official method of handling diseased animals 

 — housing and almost immediate slaughter — gives few oppor- 

 tunities for virus to spread, ramifications in the direction of a 

 strong prevailing wind have been occasionally observed to a 

 distance of a few miles, and no ordinary communication could 

 be traced by the minutest inquiry. Having regard to the distance 

 which volcanic dust can be borne in the air it seems reasonable 

 to believe that very small particles of infected mucus could be 

 carried long distances by air currents, even in clouds, and be 

 washed down in rain. The experiments of Blackley which 

 showed that the air may be heavily charged with grass pollen, 

 and that it might be carried thus as far as from Norway to this 

 country, are of some interest, and it may be remarked that 

 pollen from pastures in infected countries might be contaminated. 



Accepting air-borne virus as possible, the next question which 

 arises is, whether there exists more frequently anything in the 



