160 DISEASES OF SWINE 



the animal may be, the easier it is for him to take cholera. In other 

 words, the young animals are more susceptible, that is, they have 

 less power to resist the virus of cholera, and so they get sick quicker 

 than the old sows do, because these older animals seem to have 

 more resistance. It is very much the same in human beings 

 with many diseases. For instance, diphtheria will very quickly 

 attack a child, while a grown-up person may be able to fight off 

 the disease entirely ; in fact, it is seldom that men or women get 

 diphtheria after they are twenty years old. 



How Resistance Can Be Increased. — Old sows are especially 

 resistant to cholera germs, and, as was the case in this herd, many 

 of them pass through an outbreak of cholera without even showing 

 any signs of being sick at all. I have seen cases where every shoat 

 and pig on the place died, but the old sows came through in pretty 

 good shape. This is not always true, of course, and very often the 

 disease is so severe that it wipes out old hogs and shoats alike, and 

 leaves the pens entirely bare. This resisting power against cholera 

 can be very much built up by the use of scrum, and especially the 

 serum-simultaneous treatment. By proper use of this means of 

 increasing resistance to cholera we hope some day to be able to wipe 

 out the disease entirely, by getting the resistance of all the hogs 

 in the cholera belt so strongly developed that the germs will not 

 be able to make them sick. 



At the United States Government serum plant in Ames, Iowa, 

 the young shoats used for the production of virus with which to 

 inject the hogs from which serum is obtained receive a deep injec- 

 tion of pure hog-cholera blood deep into the muscles or meat on 

 the inner side of the hams. In this way the pigs receive a sure 

 infection with cholera, and they begin to get sick, as a rule, about the 

 afternoon of the fourth day or some time during the fifth day after 

 they have been injected. When these pigs are killed on the fifth 

 or sixth day they are bled so as to get the virus to inject other 

 animals and produce serum. They are then cut open and exam- 

 ined, and in practically every case they show signs of cholera both 

 in the organs of the abdominal cavity and in the chest. 



In this work at the Ames plant there are several reasons why 

 the disease should make its appearance so regularly on about the 

 fifth day. In the first place the pigs used for this virus production 



