GENERAL SUMMARY OF USE OF SERUM 417 



perature received the serum alone. In those that showed a nor- 

 mal temperature the serum and virus were injected. After the 

 administration of the treatment only 6 animals of the herd were 

 lost." 



This experience was a most interesting one, and shows a couple 

 of very valuable points: 



In the first place, the treatment which was originally given as 

 a simultaneous or serum-virus treatment was evidently not a simul- 

 taneous treatment at all. It is certain that the virus used in this 

 case was no good. It was probably not virus blood at all, but 

 simply blood from a healthy hog or, even more likely, was serum 

 put up in virus bottles and sent out to be used as virus. This is a 

 trick that has been practised by those who are making a poor grade 

 of serum, and do not want to trust their serum for use against real 

 virus. They simply send out the serum and with it bottles labeled 

 "virus," which do not contain virus at all. 



The development of a permanent immunity- from the use of 

 the double treatment depends as much upon the virus as it does 

 upon the serum. Both must be of proved quality and strength. 

 The virus must be capable of stimulating the cells to action in 

 order that they may take up the work of manufacturing the germ- 

 destroying bodies which are to protect the animal for the balance 

 of its hfe. 



If the substance used as virus is not a true virus at all, but 

 simply serum or healthy blood, it will not start up a reaction in the 

 tissue cells, and no germ-protecting bodies will be formed. As a 

 result, as soon as the effects of the serum itself have worn off, the 

 hog again becomes unprotected, and, as in the case of this herd, it 

 will develop the disease. 



In this herd the period of immunity lasted for about seven weeks. 

 This is about the average immunity period for the single method of 

 treatment. It is somewhat questionable if the serum originally 

 used in this case was very strong in its protective power. If a 

 good serum had been used the protection might have extended over 

 a longer period of time. 



In the second treatment, which was administered by Dr. 

 Sihler, the rule was followed which has been laid down in this work : 

 Inject serum alone in those animals which show that they are al- 



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