140 BIOLOGY OF PNEUMOCOCCUS 



ditions, such as surface cultivation on unsuitable media, incuba- 

 tion at 39°, and too long-continued drying. The same conditions 

 also led to loss of virulence. The changes noted consisted in a 

 marked decrease in agglutinability with homologous serum and in 

 the appearance of an enhanced agglutinability with heterologous 

 serums. The modified strains were, at times, agglutinable by anti- 

 streptococcic serum. The changes appeared irregularly and sud- 

 denly and did not parallel the degree of decrease in virulence. An 

 immune serum obtained after immunization with an atypical strain 

 agglutinated only that specific variant and not the parent strain. 

 In the discussion which followed the presentation of papers on 

 bacterial variability before the German Association of Microbi- 

 ology at Gottingen in 1924, Neufeld 979 reported a change in bile- 

 solubility of pneumococcal variants, as well as in their suscep- 

 tibility to optochin. In the same year, Felton and Dougherty 420 

 observed that pneumococci when grown in plain broth in an auto- 

 matic transferring device suffered a loss of virulence which was 

 directly proportional to the change in the hydrogen ion concentra- 

 tion of the medium — the more acid the medium the greater the loss 

 of virulence. Accompanying the change in virulence there was an 

 alteration in the behavior of the organisms toward agglutinating 

 serums. Although specific, the agglutinability of the modified 

 strains became greater than that of the parent organism. 



COMPOSITE CULTURES 



Amoss 12 in 1925 published an article on the composite nature of 

 a pure culture of virulent pneumococci from which he derived sev- 

 eral strains by the Barber single-cell technique. These were culti- 

 vated in broth containing Type I antiserum, and the pure culture 

 was submitted to successive transfers in bile broth and acid broth. 

 Amoss reported that the virulent strain of Type I Pneumococcus, 

 after being passed through 190 mice, was composed of individuals 

 possessing characters differing from those of the original culture. 

 A pure-line strain derived from a single cell isolated from a viru- 



