THE STREPTOCOCCI 427 



advantageous that media for this purpose should contain ascitic 

 fluid or serum. The first to obtain streptolysin in this was 

 Besredka. 85 The nature of the filter used for this purpose makes 

 a considerable amount of difference, and it is stated by De Kruif 

 and Ireland 80 that the Maassen filters are the most suitable ones, 

 and that even with these considerable amounts of hemolysin are lost 

 in filtration. According to Besredka, Braun 87 and others, the strep- 

 tolysin is not a very stable substance, and for this reason it is 

 necessary to filter the cultures at a point of optimum growth. The 

 same observation has been made by M'Leod 88 who obtained the best 

 results by filtering serum broth cultures after sixteen to eighteen 

 hours' growth. A careful experimental study of the substance has 

 recently been made by DeKruif and Ireland in the paper cited 

 above. They paid particular attention to the correlation of strep- 

 tolysin production to the logarithmic growth curve of the organisms. 

 The broth used by them in most of their experiments consisted of a 

 2 per cent pepton beef infusion broth, brought to a of 7.8 withp^. 

 sodium carbonate. To this broth, following the methods of M'Leod 

 and others, animal serum in various concentration was added. The 

 best yields were, obtained with sheep serum at a concentration of 

 20 per cent, although similar concentrations of human and rabbit 

 serum gave good yields. 



By avoiding filtration and using the high-power centrifuge, the 

 ordinary loss of hemolysin incident to filter adsorption can be 

 avoided. The hemolytlc effects can then be titrated against various 

 types of red corpuscles by adding the supernatant fluid or filtrate 

 in graded quantities to 0.5 c.c. of a 2.5 per cent suspension of washed 

 cells. 



De Kruif and Ireland's results, in the main, confirm the observa- 

 tions of others, namely, that the hemolysin appears early in the 

 cultures, and when the broth flasks are seeded with young agar 

 cultures the peak may be reached at from seven to eight hours. 

 When the crest of the growth curve has been passed, the lysin 

 begins to decrease and may disappear completely in fourteen hours. 



According to Braun, the streptolysin is extremely sensitive to 

 heat. Six hours exposure at 37 seemed to destroy it. Six hours 



a, Ann. de 1'Tnst.Past., 15, 1901, 880. 

 M Di'Kmif and Ireland, Jour. In foe. Bis., 20, 1920, 285. 

 * Rr<niii, Out. f. P.akt., 62, 1912, 383. 

 "* M'Leod, Jour. Pathol. and Baeter., 16, 1912, 321. 



