114 Bulletin 250. 



When the disease is local, it often requires a very long time for it to 

 invade the organs sufficiently to cause the death of the animal. It may 

 happen that the germs of the disease are lodged in some organ, like a 

 lymphatic gland, that is not absolutely necessary for the life of the animal 

 and the entire organ may be destroyed without apparent injury to the 

 individual. If the diseased process is arrested before it has advanced too 

 far, even when it is in a vital organ, such as a lung, the liver, or the kid- 

 ney, the animal will continue to appear to be perfectly sound. Animals thus 

 affected are thought to be perfectly well, as they appear to be, but sooner 

 or later the disease becomes more extensive. It often happens that the 

 disease becomes arrested or temporarily healed, and remains so for a con- 

 siderable time, one, two or three years and even longer, when it may start 

 up again. Frequently, animals that are in a period of incubation or 

 that contain foci of arrested disease and which appear to be perfectly well, 

 are bought in good faith and placed in a healthy herd with the result that 

 they bring the disease and not infrequently transmit it to other animals. 

 Various manifestations of the disease are seen in Figs. 129-132. 



It is very likely that some animals, especially cattle, are infected and 

 recover. This is to be expected in some cases where they are kept under 

 favorable hygienic conditions. At present, however, our knowledge of 

 recovery from tuberculosis in cattle is too meagre to warrant much en- 

 couragement from this source. It is safer and more economical not to 

 trust to a recovery. An animal that once reacts must be considered sus- 

 picious thereafter. However, a few such animals remain well until they 

 die from other causes. 



5. How to detect tuberculosis in cattle. 



From what has been said about the course of the disease, it is perfectly 

 clear that there may be a large number of animals in a herd that are 



amount of tuberculous matter and the number of tubercles, and may apply to a 

 case which is confined to one of the body cavities. 



(i) The carcass may be passed when the lesions are limited to one group 

 of lymphatic glands or one other organ. 



(2) The carcass may be passed when the lesions are limited to two groups 

 of visceral lymphatic glands in either the thoracic or the abdominal cavity. 



(3) The carcass may be passed when the lesions are limited to two visceral 

 organs (other than lymphatic glands) in the thoracic or the abdominal cavity, 

 provided the lesions are slight, calcified, and encapsulated.^ 



(4) The carcass may be passed when the lesions are limited to one group of 

 visceral lymphatic- glands and one other organ in the thoracic or abdominal cavity, 

 provided the lesions in the affected organs are slight. 



(5) The carcass may be passed when the lesions are confined to two groups 

 of visceral lymphatic glands and one other organ in the thoracic or the abdominal 

 cavity, provided the lesions are slight, calcified, and encapsulated. 



(6) The carcass may be passed when the lesions are confined to the lungs, 

 the cervical Ivmphatic glands, and one group of the visceral lymphatic glands of 

 the thoracic cavity, provided the affection is slight and the lesions are calcified 

 and encapsulated. 



(7) The carcass shall be condemned when well-marked lesions are discovered 

 in both the thoracic and the abdominal cavity. 



