BACTERIOLYTIC SERUMS IN THE TREATMENT OF DISEASE 381 



When the whole series of pipets has been dealt with in similar fashion 

 they are returned to the incubator for another twenty-four hours. 



Reading the Result. The continued sterility of the broth may be de- 

 termined from direct naked-eye inspection. 



When a complete bactericidal effect has been secured, the broth will 

 have undergone no color change, but will still be clear. 



When a growth of the typhoid bacillus has occurred, a perceptible 

 cloudiness will be apparent in the broth, and the color will have changed 

 from blue to reddish-blue, indicating that acid has been formed from the 

 mannite. 



Turbidity of the broth without a change of color would indicate the 

 admission of contaminating microbes that were unable to split mannite 

 with the formation of acid. 



The controls are first examined and recorded. All the culture con- 

 trols should show a growth and change of color. The serum controls 

 should be sterile; the normal serum controls may or may not be sterile, 

 depending upon the amount of natural bactericidal amboceptors which 

 it contains for the test organism. 



The pipets containing the patient's serum are now examined, and a 

 simple numeric expression for the result is obtained by referring to the 

 result of the enumeration of the various dilutions, as determined by the 

 counting of the plates. In this manner the number of bacteria contained 

 in 1 c.c. of the lowest dilution of the bacterial culture that has been com- 

 pletely sterilized is calculated. This will give the number of micro- 

 organisms which 1 c.c. of serum would be capable of killing. 



Although this test affords a convenient basis for the comparison of 

 serums, it must be understood that the expression is entirely arbitrary, 

 and will vary according to the culture employed; this is true of any 

 technic for determining the bactericidal titer of a serum. 



BACTERIOLYTIC SERUMS IN THE TREATMENT OF DISEASE 

 While bacteriolysis is readily demonstrated with some bacteria both 

 in vivo and in vitro, nevertheless, when such serums are used thera- 

 peutically, beneficial results are not dependent solely upon lysis of the 

 infecting bacterium, but are usually the result of a combination of lysis 

 with increased phagocytosis, due to the simultaneous presence of bac- 

 teriotropins (immune opsonins). When one recalls the close similarity 

 in general properties that exists between bacteriolysins and bacterio- 

 tropins, the difference between extracellular and intracellular lysis is 



