EXPERIMENT STATION BULLETINS. 439 



On the whole, however, it is to be observed that a serum having a 

 high agglutinative power can be expected to have a higher potency 

 than a serum with low agglutinative power. By potency we mean that 

 the serum was able to protect a small pig against 1 cc. of virulent 

 hog cholera blood in doses not larger than usually recommended by 

 those engaged in serum production. 



It may be well to arrange the mixed sera according to their agglutina- 

 tive power and potency. 



Of those agglutinating at 



1 — 50,000 5 or 100 per cent were potent. 



1 — 12,000 5 or 83 J per cent were potent. 



1 or 16| per cent was not potent. 

 1 — 8,000 4 or 100 per cent were potent. 



1 — 5,000 1 or -100 per cent was potent. 



1 — 4,000 7 or 77 7-9 per cent were potent. 



2 or 22 2-9 per cent were not potent. 

 1 — 2,000 8 or 80 per cent were potent. 



2 or 20 per cent were not potent. 

 1 — 1,000 1 or 50 per cent was potent. 



1 or 50 per cent was not potent. 

 1 — 800 1 or 50 per cent was potent. 



1 or 50 per cent was not potent. 

 1 — 400 2 or 50 per cent were potent. 



2 or 50 per cent were not potent. 

 Less than 1 or 33 1-3 per cent was potent. 



1 — 400 2 or 66 2-3 per cent were not potent. 



Of all the mixed sera agglutinating at a dilution of 1-2,000 or above 



85.71 per cent were potent. 

 14.28 per cent were not potent. 



Of all the mixed sera agglutinating at a dilution of 1-1,000 or less, 



45.45 per cent were potent. 

 54.54 per cent were not potent. 



A very potent serum, such as mixed serum 46 requires onh- 5 cc. 

 to protect a 36 lb. pig, yet agglutinates at only 1-400. Mixed serum 

 57 agglutinating at 1-50,000 requires that 15 cc. shall be injected to 

 protect a 22 lb. pig. 



After studving the matter verv carefuUv, we have come to the con- 

 elusion that the biological test (using snmll pigs) is very uncertain. 

 Our experience shows that potency may be indicated if pigs weighing 

 75 to 100 lbs. be used, while lack of potency may be indicated by the 

 use of pigs just weaned. The involvement of ascarides, lung worms 

 and unfavorable climatic or dietary conditions tend to make serum- 

 testing on small jjigs very unsatisfactory. 



Potencv as indicated bv our biological tests is onlv a relative and 

 more or less uncertain matter. Therefore, when we try to compare the 

 results of an easily controlled in vitro test such as the agglutination 

 reaction with a very elastic standard of in vivo testing confusion is sure 

 to ensue. Moreover, we have to admit at the outset that we are dealing 

 with an unknown quantity when we try to introduce B. clioJerae swis 

 into the subject of potency of serum. We have not yet found an answer 

 to the ;ill important question: ''What has B. cholerae suis to do with 



