CONTAGIOUS PLEURO-PNEUMONIA IN CATTLE 415 
The period of incubation is, after the subcutaneous injection of the 
virus, from 6 to 27 days and after inhaling it from 12 to 16 days, 
according to Nocard and Roux. 
Symptoms. The symptoms are such as would be expected with 
inflammation of the lungs and pleura, but they vary considerably 
according to the course which the disease runs. If the attack is an 
acute one, the symptoms appear suddenly. The breathing becomes 
rapid and difficult, the animal grunts or moans with each expiration, 
the shoulders stand out from the chest, the head is extended on the 
neck, the back is arched, the temperature ranges from 104 to 107° F., 
the milk secretion is suspended, there is loss of appetite, rumination 
is stopped, the animal may bloat and later be affected with a severe 
diarrhea. 
Very often the attack comes on slowly and the symptoms are more 
obscure. In the milder cases there is a cough for a week or two but 
no appreciable loss of appetite or elevation of temperature. The 
lungs are but slightly affected and recovery soon follows. Such ani- 
mals may disseminate the virus for a long time without being suspected 
and for that reason are very dangerous. 
In more severe cases the cough is frequently more or less painful, 
the back somewhat arched and the milk secretion diminished. The 
inflammation of the lung does not, as a rule, subside and the organ 
does not return to normal condition as in ordinary pneumonia, but 
with this disease the affected tissue dies and a fibrous wall is formed 
around it. These sequestra may later break and discharge into 
bronchi, thereby eliminating the virus. The tissue, thus encysted, 
gradually softens and becomes disintegrated into a purulent-like sub- 
stance. The recovery, therefore, is only partial. 
The urine is dark in color and acid in reaction. It is passed at long 
intervals. 
Seriously affected animals remain standing if they have sufficient 
strength, but those which lie down are said to always lie on the affected 
side. . 
The proportion of animals that become affected after being exposed 
varies according to the virulence, the susceptibility of the animals and 
the length of time during which exposure is continued. Sometimes 
not over 15, 20 or 30 per cent. of the animals exposed will contract the 
disease, while at other times 80 or 90 per cent. may be infected. 
Some of the earlier writers supposed about one animal in four was 
‘immune. The mortality may not exceed 10 per cent. and it may 
