CLINICAL EVIDENCE OF VALUE OF SERUM 453 



cially does this hold true in those cases where a sufficient dose of 

 serum is given with the virus to fully protect the animal, and pre- 

 vent any of the treated animals from developing any signs of 

 illness. 



With a properly made serum and a reUable virus I do not 

 think there can be any question but what it can be given with 

 perfect safety, if the dose of the serum is made large enough to 

 afford proper protection against the dose of virus used. It will 

 be noted that in practically all the experimental herds treated 

 in this series the dose of virus used was double that usually given, 

 while the doses of serum given were not quite up to the doses usually 

 recommended for animals of the same weight. These herds, 

 then, are an unusually severe test of the efficiency of the serum 

 as a protection against the development of infection following 

 the use of virus blood, and the few unfavorable results recorded 

 are, in my opinion, as much due to this fact as any other. 



It is plain that the resistance of all hogs to cholera is not the 

 same. Some individuals take the disease more readily than others. 

 With herds that have a very weak resisting power to the dis- 

 ease, as in the case of the animals described in Herd Number 11, 

 it is plain that the injection of a large dose of virus with a small 

 dose of serum would be likely to produce disease that would not 

 occur if a smaller dose of virus was given and a large dose of serum. 



Herd number sixteen of this experimental series was located in 

 Section 23 of Grant Township, Story County, Iowa. The herd was 

 made up of a number of old sows and shoats, running all sizes and 

 ages. 



This herd, as in the case of a number of those just described, 

 was located in the center of an infected district. The experiment 

 was started on this farm October 16, 1907. At this time the 

 appearance of the herd was good, and there was no sign of cholera 

 in any of the animals. 



Thirty-five shoats, whose average weight was about 80 pounds, 

 were injected with 20 c.c. each of serum, plus 2 c.c. of virulent 

 blood. The virus blood used in this herd was the same as that 

 used in Herd Number 14. Seven more shoats, with an average 

 weight of 40 pounds, received each 20 c.c. of serum with no viru- 

 lent blood. Fifteen small shoats, weighing 25 pounds each. 



