274 EXPERIMENT STATION EECOKD. [Vol.43 



repeated inoculations showed the presence of bacteriolytic and agglutinating 

 antibodies, and the animals showed more or less active immunity to the in- 

 jected bacteria. Titration of the blood serum before and after the produc- 

 tion of this active immunity gave practically the same results for complement 

 titer. 



In a comparative test of the resistance to infection of nonimmunized com- 

 plement-deficient and complement-normal guinea pigs, 77 of 100 complement- 

 deficient animals succumbed to the inoculation of live cultures of Bacillus 

 cholerce suis, while only 20 of 100 similarly inoculated complement-normal 

 animals died. This is thought to indicate that deficiency in complement is 

 associated with deficiency in natural resistance to bactei'ial infection. 



The phagocytic index of the serum of complement-deficient guinea pigs was 

 found to be about one-half that of the complement-normal animals. 



The determination of the number of bacteria in pure cultures, G. 

 DiCHTL {Arch. Hyg., 89 (1920), Nos. IS, pp. ^7-62).— A study of the effect of 

 various factors on the accuracy of the method of estimating the number of 

 bacteria in a su.spension from the volume of the sediment on centrifuging is 

 reported. 



The water content of the agar serving as a culture medium was found to 

 have no influence on the results. The period and temperature of incubation 

 affected the results to the extent that young cultures contained more living 

 organisms than old cultures, and that at a temperature of 22° C. the number 

 of organisms remained at its maximum longer than at higher temperatures. 



The sedimentation method is recommended as being simple and easy to 

 manipulate, and as accurate as the more tedious counting method. 



A method of standardizing bacterial suspensions, F. L. Gates (Jour. Expt. 

 Med., 31 {1920), No. 1, pp. 105-1 IJf, fi[/s. 3). — The method described is based upon 

 the observation that if a wire loop is gradually pushed down into a bacterial 

 suspension, the depth at which the loop disappears will be determined by the 

 opacity of the supervening column. An instrument is described by means of 

 which the density of suspension or the number of bacteria may be measured 

 by the length of the column of suspension required to cau.se the disappearance 

 of a wire loop. 



In using this method standards should be marked out for each observer by 

 a comparison of the corrected depth of disappearance readings and the corre- 

 sponding bacterial count. It is claimed that when such standards are estab- 

 lished suspensions of the same organism can be estimated rapidly. 



A plea for standard method of estimating the number of killed bacteria 

 in suspension, W. E. King and R. E. Vories {North Amer. Vet., 1 {1920), No. 

 1, pp. 13-18). — The authors describe briefly the method of estimating the ap- 

 proximate number of bacteria in a given suspension described by Hopkins (E. 

 S. R., 30, p. 780) and the one by Gates noted above, and present tables giving 

 a comparison of the bacterial count of several well-known commercial vaccines 

 as determined apparently by one of the above methods and the count as stated 

 on the label. 



The discrepancy in these figures and the irregular results obtained in inocu- 

 lation experiments indicate, in the opinion of the authors, the necessity of 

 the adoption of some standard method for the determination of the number of 

 killed organisms in suspension. 



The transmutation of bacteria, S. Gueney-Dixon {Cambridge: Univ. Press, 

 1919, pp. XVIII+n9; rev. in Brit. Med. Jour., 3087 {1920), pp. 297, 298).— In 

 this monograph the author discusses, on the basis of the literature and of ex- 



