STUDY OF ANTISTREPTOCOCCUS SERUM. 119 



B. coli, all of which are found to clump when placed in contact 

 with a specific serum. 



Although the agglutination of the streptococcus by its preventive 

 serum is generally distinct, it is never very marked; to cause it, 

 large quantities of serum are necessary, at least one-third the 

 volume of the culture fluid. Not all of the chains of the strepto- 

 cocci are affected; some of them remain separate. Cultures of 

 streptococci grown in preventive serum or in a fluid containing a 

 certain amount of it (for example, equal parts of bouillon and 

 immune serum) show only a slight grouping of the organisms at 

 best. In short, preventive serum causes no profound alteration in 

 the streptococcus. The growth of the organism is not sensibly 

 diminished and its morphology remains the same, with the excep- 

 tion of certain variations in the length of the chains. And even 

 the agglutinating property that has been found by recent studies 

 to be present in numerous immune sera is only slightly developed in 

 antistreptococcus serum. 



We must consider whether a preventive serum with so slight an 

 effect on the morphology and development of the streptococcus 

 does not have some weakening influence on its virulence. Cul- 

 tures of streptococci grown in a mixture of equal parts of preven- 

 tive serum and pepton bouillon retain a very great virulence, as 

 may be determined by comparing them with cultures made on 

 bouillon plus normal horse serum. After 24 hours' growth in an 

 incubator the turbid culture fluids are filtered through filter paper. 

 There remain enough bacteria on the filter paper and they may be 

 washed and freed of serum. A small amount of these bacteria is 

 taken with sterile forceps and suspended in a few cubic centimeters 

 of salt solution. Two emulsions are thus obtained, both slightly 

 and as near as possible equally turbid: one containing bacteria 

 cultivated in normal serum and the other bacteria cultivated in 

 preventive serum. Both these fluids are extremely virulent, al- 

 though they contain few bacteria; 0.0005 of a cubic centimeter of 

 either one kills a rabbit in 24 hours. In other words, there has 

 been no detectable attentuation by growing in preventive serum. 



And, what is more, the whole culture containing preventive serum 

 and bacteria is also very dangerous for rabbits, killing them as 

 rapidly as controls, that is, in 24 hours. 



