PREDISPOSING CAUSES 101 



liable to contract the disease, and, if they do develop cholera, they 

 are less likely to die from the attack. 



(3) Pregnancy. — To a slight degree pregnancy seems to protect 

 the animal from attack, although a sow will often abort her litter 

 without herself showing very marked symptoms of the disease. 



(4) Breed. — This is a subject which has led to many long-drawn- 

 out arguments among the exponents of the different standard 

 breeds of swine. Each breed has enthusiastic followers, who be- 

 lieve that animals of that particular breed are less susceptible to 

 cholera, but close investigation fails to show any- marked resisting 

 powers on the part of any particular breed. A few years ago 

 breeders of the Mulefoot hog claimed to have found in this 

 breed a type of hog that was proof against cholera, but stock 

 raisers all over the hog-raising belt have found that these claims 

 were exaggerated, and comparatively few of this type of animal are 

 now to be found in the large hog lots of the Central West. 



It has been fairly conclusively proved, however, that standard 

 bred animals are more resistant to this type of infection than are 

 the grade animals. This apparent resistance is in large measure 

 no doubt due to the fact that standard bred animals are usually 

 handled under better sanitary surroundings, owing to their higher 

 cash value, and hence are not subject to as many opportunities 

 for infection. 



It has been my observation that Poland-China, Duroc-Jersey, 

 Berkshire, Chester-White, and other standard types of swine ap- 

 pear to all be about equally lacking in immunity to the virus of 

 hog-cholera, and animals of all these breeds may be found on 

 funeral bonfires in our hog-raising communities during an out- 

 break of the disease. 



(5) Season. — Cholera is a disease that may be regarded as 

 present in certain regions of the United States at all seasons of the 

 year, but there are certain parts of the year when the number of 

 cases show a marked increase in number and when the disease seems 

 to light up with renewed vigor. There are a number of reasons 

 why this should be so, as I will attempt to explain: 



About the first of May the gradual increase in cases usually 

 begins, and this steadily creeps upward during the early summer, 

 to reach a point in midsummer when the incidence of the disease 



