EXPERIMENT STATION BULLETINS. 433 



In Table XXV there are found in parallel columns the results of 

 the tests and subsequent retests of 25 mixed sera. Tables XXIII and 

 XXIV show the dates of the respective tests and retests. It is seen 

 that the retests were made 6-8 months after the first tests. 



The retests show 



In 7 cases no change in agglutinative power. 



In 4 cases a 25 per cent decrease. 



In 3 cases a 50 per cent decrease. 



In 1 case a 68 per cent decrease. 



In 5 cases a 75 per cent decrease. 



In 1 case a 80 per cent decrease. 



In 4 cases an apparent increase. 



Any increase is probably only apparent. In case of mixed serum 

 30 the first test failed to establish a maximum showing only that it was 

 less than 400, The first test with mixed serum 31 probably did not 

 establish a maximum since no test was made between 400 and 800. The 

 same is true with mixed sera 37 and 44 when no attempt was made 

 to get a reaction above 1-12,000. 



We have not found that the presence of carbolic acid, trikresol 

 or foiTualin has any depressing effect upon either the agglutinative 

 power or potency of hog cholera serum. 



AGGLUTINATIVE POWER AND POTENCY. 



The question as to whether we can turn the agglutination test to 

 account in measuring the potency of serum is answered in Table XXV. 

 It must be confessed that the answer is not very definite. Table XXV 

 shows the agglutinative power of the sera and the results of the bio- 

 logical tests. There are given the different amounts of serum used, 

 the weight of the pigs employed and the results. In all cases the serum 

 was tested against 1 cc. of virulent hog cholera blood. The virulence 

 of the blood was always determined by the use of check pigs corre- 

 sponding in weight, thrift and origin to the test pigs. 



It would be possible to pick out a number of cases of mixed sera that 

 showed low agglutinative power and low potency, and it would be 

 easy to pick out cases showing a high agglutinative power and high 

 potency. If we could arrange all the cases under these two headings 

 the matter would be answered very satisfactorily but we can find cases 

 of low agglutinative power and high potency and those showing high 

 agglutinative power and low potency. 

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