492 BACTERIOLOGY. 



human sepsis, which are not very virulent in animals, 

 are especially in need of investigation. If those who 

 use the serum will send to the laboratories materials 

 for cultures this can in time be fully determined. 



The Preparation of the Serum. Antistreptococcus 

 serum is obtained from the horse, ass, and sheep after 

 treatment by repeated injections of living streptococcus 

 cultures. The procuring of a serum of the highest 

 potency requires a considerable number of animals, for 

 some produce with the same treatment a more protec- 

 tive serum than others. The serum must be sterile 

 from streptococcus as well as from other contaminations. 



The Stability of the Serum. Unfortunately, after sev- 

 eral weeks or months, the serum, as a rule, at least, loses 

 its protective value. It should be kept in a cold and 

 dark place. Not only ourselves, but others, such as 

 Aronson, have found this to be true. 



To this deterioration can probably be ascribed the 

 failure of Koch, Petruschky and others to find in the 

 serum any power to protect animals from infection. 



The Standardization of the Value of the Serum. The 

 value of the serum is measured by the amount required 

 to protect against a multiple of a fatal dose of a very 

 virulent streptococcus. The dose is usually a thousand 

 times the average fatal amount of a very virulent 

 streptococcus. 



This method gives, as a rule, to those unfamiliar 

 with bacteriology an exaggerated idea of the potency 

 of the serum. 



A thousand times the amount of a very virulent 

 streptococcus culture required to kill an animal by 

 producing septicaemia is still too little to kill by the 

 streptococci injected; it is only their enormous multi- 

 plication in the animal which kills. 



