232 VETERINARY HYGIENE 



taken from the official returns, together with the calculated annual 

 loss, and this loss expressed in units per 100,000 is given in the 

 following table : 



Cows and Heifers. Loss per annum. Loss per 100,000. 



England 2,184,615 5,292 242.2 



Scotland 453,703 1,224 269.8 



Wales 299,605 300 100.1 



Ireland 1,638,929 1,406 85.7 



Such figures do not afford any true indication of the prevalence of 

 the disease in this country, but merely represents what is probably 

 but a rough estimate of the cows and heifers affected with the tuber- 

 culosis of certain types, and that only for the period given. 



Tuberculosis is more prevalent in city byres than in country 

 ones, this being partly attributable to the fact that practically none 

 of the former are self-contained but are continuously changing 

 their stock, and must perforce buy in the open market without any 

 guarantee of freedom from infection. 



It follows from what has been said before that housed cattle 

 are more commonly affected and, according to Hutyra and Marek, 

 the disease is practically unknown on the prairies of North America 

 and on the steppes of Eastern Europe. According to some writers, 

 however, the disease is met with even among cattle which spend 

 the greater part of their lives in the open air. For instance, Russell* 

 states that he has noted several instances in which range cattle which 

 had never been housed were found to be badly affected. Bang, 

 in his report to the Seventh International Veterinary Congress, 

 states that " it is certain that often in the open air infection is not 

 excluded, especially when the cattle are free to run about and lick 

 one another, and when several animals are allowed to drink from 

 the same vessel." 



The period of incubation for tuberculosis is usually prolonged, 

 but it is variable and uncertain. Months or years may pass before 

 an affected animal shows clinical symptoms of the disease. 



The organism remains virulent outside the body for a con- 

 siderable period if in a suitable environment. Its resistance in 

 the face of different agencies is shown by the following 

 examples! : Cadeac and Malet found tubercle bacilli to be still alive 

 and virulent in putrefied cattle lung after 167 days. Schill and 

 Fischer noted dry sputum protected from light to be virulent for 

 126 days. Desiccation per se is therefore not a destructive agency. 



* Bovine Tuberculosis, Devine, Chicago, 1917, p. 15. 

 t Hutyra and Marek, Spec. Path., Vol. I., p. 507, Trans. 



