56 APPLIED IMMUNOLOGY 



potent antistaphylococcic serum has possibly been due 

 to utilization of avirulent or univalent cultures of the 

 organisms. One of the most important factors con- 

 ducive to the successful production of this serum is the 

 employment of staphylococcus cultures from many 

 sources. With this essential in mind, one of us 

 (Thomas) isolated eighteen strains of Micrococcus 

 aureus in pure culture from many sources, as fur- 

 uncles, carbuncles, abscesses of the scalp, thoracic 

 empyema, axillary abscess, and septicaemia. From 

 these strains 24-hour cultures were grown and from 

 the mixed growth a suspension in physiologic salt 

 solution was prepared containing 32,400,000,000 cocci 

 to the cubic centimetre. This was then heated for one 

 hour over a water-bath at 60° C. The animal selected 

 for the purpose of immunization was a full-grown ram 

 weighing 165 pounds. The degree of immunity of 

 the animal was governed by determination of the 

 opsonic index for the polyvalent staphylococcic sus- 

 pension (see Fig. 3). At the first injection the ram 

 received intraperitoneally 972,000,000,000 dead sta- 

 phylococci. Thereafter at weekly intervals either grad- 

 ually increasing doses, or slightly smaller doses heated 

 for a shorter time, and finally unheated organisms, were 

 injected. After twelve inoculations, the index was 

 found to be 2.6, and the animal was bled to death 

 from the carotid artery. The serum was hermetically 



