INCUBATION PERIOD OF CHOLERA 155 



membrane (endocardium) and sometimes beneath the external 

 covering (pericardium) . 



(9) The Lungs. — The findings here are very unreliable in char- 

 acter. In some cases we have merely petechial hemorrhages 

 beneath the pleura, which appear as pin-point-Uke dots of discol- 

 oration. In other cases we may have all the lesions of a typical 

 pneumonia, with consolidation of the lung, absence of air, and all 

 the usual changes described under pneumonia. In these cases, 

 especially where abdominal lesions are slight or absent, absolute 

 diagnosis is difficult without experimental injection of healthy 

 young animals. 



(10) The Bones. — The changes in the bones, while rarely ob- 

 served in the regular postmortem made on the farm, are none 

 the less interesting and characteristic. There is no other condition 

 in which the hemorrhagic changes in the bones are quite so promi- 

 nent and well marked, and on the meat-inspection floors of our 

 large packing houses the hog-cholera spine is commonly observed. 



INCUBATION PERIOD OF CHOLERA 

 Definition. — By "incubation period" is meant the length of time 

 which it takes for an animal which has been exposed to the disease 

 to begin to show signs of being sick. The number of days which it 

 will take for an animal to get sick will differ quite a good deal in 

 each case, depending upon the amount of resistance the animal 

 offers against the disease, the number of germs entering the body, 

 and the virulence or disease-producing power of the germs present 

 in this particular outbreak of the disease. 



Some hogs seem to take the disease very, very easily, and it 

 takes only a small amount of virus or germs to get the disease 

 started in a herd of this kind. This is very likely to be found 

 the case in young animals, and in those hogs who are run down for 

 any of the reasons which were mentioned under Predisposing Causes. 

 In a hog that is in a run-down condition the germs of cholera have 

 an unusually easy time once they get into the body. They breed 

 quite rapidily, and it is only a short time until there are enough 

 of them present to cause the animal to show signs of being sick. 

 It is in cases like this, where the herd is made up of young shoats, 

 or where, for any reason, the health of the animals is rather poor 



