DISEASES OF CATTLE 349 



■hours after injection. It should remain practically at a maxi- 

 mum for two hours or more and gradually subside. When it 

 reaches 104 degrees or more and is maintained for some hours, 

 the animal is regarded as tubercular, if no fever was shown 

 before the injection. Sudden rises for a short time only do not 

 indicate a reaction. The rises of less than 1.5 degrees do not 

 indicate a reaction. In all cases of doubt, the animal should be 

 separated from the herd and retested not sooner than four to six 

 weeks (the test will not give reaction under this time). 



Retesting. — A single test of a diseased herd cannot be relied 

 upon to detect every tuberculous animal. If animals are found 

 by the first test to be affected, they should be tested again in four 

 to six weeks. Even in those herds in which no reacting animals 

 are found, it is a good plan to test once each year. 



Tuberculin not infallible. — While tuberculin is the best 

 method known for detecting tuberculosis, it is not infallible. On 

 the average if properly handled, it will detect 97 per cent of the 

 cases. In some cases, especially when the animals are badly 

 diseased, it fails to react, and in a very few cases it seems to cause 

 a rise of temperature in healthy animals. 



Prevention of tuberculosis. — In the beginning of this discussion 

 it was stated that tuberculosis is a communicable germ dis- 

 ease, and therefore preventable. In order to prevent, infected 

 animals must not be brought into healthy herds, for as we have 

 observed diseased animals spread the infection wherever they go. 

 Much space has been given to methods of locating the disease in 

 order that those herds already free may not be infected by the 

 addition of an infected animal. If a herd is known to be healthy, 

 never bring a new animal into the herd until it has been tested, 

 and if there is the sUghtest doubt about its being tubercular, it 

 should be excluded. 



If in addition to the tubercuHn test and the exclusion of all 

 diseased animals, the quarters where the cattle are kept are well 

 ventilated, and well Hghted, admitting the direct rays of the sun, 



