PREVENTIVE MEDICINE 231 



animals for a brief period does not necessarily imply that the 

 former will become infected, but if the period of cohabitation is 

 extended infection is almost certain to be transmitted if the environ- 

 ment is suitable. Tuberculosis is, therefore, a very insidious 

 disease and one of very grave importance to the hygienist. 



Among the different species of animals cattle are of course most 

 frequently infected, while cases are occasionally observed in equines, 

 and one or two instances of natural infection have been recorded 

 in the sheep by M'Fadyean and others. The disease is not by any 

 means rare in the dog and cat and occasionally outbreaks are seen 

 amongst poultry. The disease is rare in goats. Tuberculosis does 

 not occur among wild animals in a state of nature, but many species, 

 and especially monkeys, suffer from the disease when kept in 

 confinement. 



Tuberculosis is universally but unequally distributed among 

 cattle, and the percentage of affected animals tends to rise in pro- 

 portion as the size of the herds increases. More cases are observed 

 in Shorthorns and Ayrshires than in any other breed. Jersey 

 cattle and Herefords, and especially the former, are particularly 

 free. The disease is also infrequently observed among Scottish 

 Highland and Welsh cattle. Pedigree strains are more susceptible 

 than common bred animals, also the incidence of the disease accord- 

 ing to age depends entirely upon the conditions in which the animals 

 are kept. It is not often seen in yearlings, and is rare in calves. 

 It is most frequent among adult cattle and especially amongst old 

 cows which for long periods have been stalled in close contact. It 

 is important to note, therefore, that the incidence of tuberculosis 

 does not run parallel with susceptibility according to age; thus, 

 though calves are almost entirely free from the disease naturally, 

 they are more susceptible than adults to experimental infection. 



No statistics of any definite value are available to show the 

 distribution of tuberculosis in the United Kingdom, but the follow- 

 ing figures calculated on fourteen months' working of the Tuber- 

 culosis Order give at least a relative idea of its incidence in the 

 different parts of the kingdom. During the period 1st May, 1913 

 to 30th June, 1914, in Great Britain there were 7952 cattle 

 destroyed as being affected with either tuberculosis of the udder or 

 tuberculosis with emaciation. This represents 6816 cattle for a 

 twelve months' period, which were distributed as follows : 

 England 441 per month at the rate of 5292 per annum 

 Scotland 102 1224 



Wales 25 300 



The number of cows and heifers in calf or in milk in June, 1914, 







