282 DISEASES OF CATTLE, SHEEP, GOATS, ETC. 



tie are excited, and nervous, a false reaction may be obtained. In 

 this way healthy cows may be wrongly adjudged tubercular. Other 

 cases classed as errors are due to the incomplete post-mortem exam- 

 ination of the animal. The disease may be located in some part of 

 the body not usually examined, such as the brain, bone marrow, 

 glands of the muscles, etc. It is usually impossible to make a thor- 

 ough examination of the entire carcass especially where the exam- 

 ination must be hurried and superficial as that done by regular meat 

 inspectors whose duty it is not to determine whether the animal ig 

 actually diseased or not, but whether the meat should be condemned 

 as unwholesome for food. 



Do All Tubercular Animals Reaet to the Test? Animals in 

 which the disease is far advanced and in which much diseased tissue 

 exists do not always react to a normal dose of tuberculin. Such ani- 

 mals, however, usually show physical signs of the disease. Animals 

 in which the disease is still in the period of incubation do not react. 

 By the period of incubation is meant the time after infection has 

 occurred, but before the disease has become established in the body. 

 In tuberculosis this period may be several months in length. 



Animals in which the disease has ceased to progress may not 

 react. Such an animal may react once, but may not react for a 

 number of subsequent tests and may then again react, because the 

 disease has been active, then dormant, and again become active. 



Do Cattle Recover From, Tuberculosis? Some animals react 

 once, but not on subsequent tests. If failure to react depends upon 

 the disease becoming dormant, such a condition might be taken to 

 indicate recovery, but so little is known concerning this condition, 

 that it is not advisable to take possible recovery into account in the 

 handling of tubercular animals. 



Does the Tuberculin Test Tell Anything Concerning the Ex- 

 tent of the Disease in the Animal? Nothing whatever. An ani- 

 mal with a single diseased gland will give as marked a reaction as 

 one badly diseased. 



THE CONTROL OF TUBERCULOSIS. 



How Can a Diseased Herd Be Freed From, Tuberculosis? Test 

 the whole herd. Remove all reacting animals. Retest all suspicious 

 animals in three months, and the entire herd again in one year and 

 annually thereafter. Disinfect the stable. 



How Can a Herd Be Kept Free From Tuberculosis? Test an- 

 nually or at least every two years, and retest all suspicious cases in 

 three months. Test every animal introduced into the herd at the 

 time of purchase, and again in three months. Use a farm separa- 

 tor or feed only skim milk and whey that have been heated. 



Is the Above Plan Certain to Prove a Successful One? No, be- 

 cause an animal in the period of incubation may be purchased, shei 

 may not react at the first or second test, and yet may before the 

 next test, 9 to 12 months later, serve to infect other cows. 



How Can the Owner Be Perfectly Certain Not to Introduce Tu- 

 berculosis Into the Herd? Buying animals only from herds known 

 absolutely to be free from tuberculosis. 



