PAUL H. De kruif 393 



pH 4,7 to 3.8 before animal passage, to pH 5.6 to 3.2 after passage 

 through three rabbits. 



Up to the present, the change in acid agglutination optimum that 

 occurs during mutation has been accompanied invariably by a great 

 loss in virulence. For example, all Type D strains tested have been 

 fatal to rabbits in doses of 10~^ to 10~^ of a serum broth culture. The 

 Type G forms arising from such strains are seldom fatal in 0.5 cc. of 

 undiluted culture. Frequently rabbits are able to resist 1 .0 cc. 



The experiment just described indicates that the decrease in stability 

 to acid does not necessarily go hand in hand with loss of virulence, 

 and certainly bears no causal relationship to such loss. For, while 

 the stability to the hydrogen ion had greatly decreased during animal 

 passage, the virulence had increased from 0.5 cc. to lO"* cc. 



SUMMARY AND CONCLUSIONS. 



A distinct difference in acid agglutination optimum for Type D 

 (bacillus of rabbit septicemia) and its mutant form. Type G, has 

 been observed. The optimum for Type D lies between pH 3.5 and 

 pH 3.0. This changes during mutation, the resulting Type G mutants 

 having in general an optimum lying between pH 4.7 and pH 3.8. 



The constancy of the optimum for Type D is very strict, while 

 that for Type G is slightly less so. The variation is never so great as 

 to cause an overlapping of optima and consequent failure of differ- 

 entiation. 



These acid agglutination optima are in the nature of physical con- 

 stants for the two types and would imply a fundamental difference 

 in the chemical constitution of the organisms. 



Animal passage, far from causing a reversion of the mutant Type 

 G to the prim.ordial Type D form, brings about a still greater insta- 

 bility in the presence of H ions. 



BIBLIOGRAPHY. 



1. De Kruif, P. H., J. Exp. Med., 1921, xxxiii, 773. 



2. De Kruif, P. H., Proc. Soc. Exp. Biol, and Med., 1921, xix, 34. 



3. Michaelis, L., Deutsch. mcd. IVocli., 1911, xx.\vii, 969. 



4. Beniasch, M., Z. Immunitiilsforsch., Orig., 1911-12, xii, 268. 



5. Sobernhcim, G., and Scligmann, E., Z. Immunildisforsch., Orig. 1910, vii, 342. 



