600 BIOLOGY OF PNEUMOCOCCUS 



inadequacy of Type III immune horse serum in the treatment of 

 lobar pneumonia caused by organisms of that serological type is 

 still one of the riddles of pneumococcal research. 



The substitution of immune rabbit serum for immune horse se- 

 rum in the treatment of lobar pneumonia holds promising possibili- 

 ties. From the experimental standpoint, antipneumococcic serum 

 produced in rabbits confers a greater degree of protection on mice 

 in proportion to the content of specifically precipitable protein 

 than does antipneumococcic serum obtained from horses. In mice, 

 small amounts of cholesterol, cephalin, or materials rich in these 

 lipids block the protective action of antipneumococcic horse serum 

 but are without effect in the case of rabbit serum. In massive infec- 

 tions in laboratory animals there are optimal amounts of anti- 

 pneumococcic horse serum which must be used in order to obtain 

 successful results. Larger amounts are less efficacious and still 

 larger amounts may have no protective action whatever. The pro- 

 zone effect is not observed with antipneumococcic rabbit serum. 



As compared with horses, rabbits almost invariably respond to 

 pneumococcal immunization with the production of serum of good 

 titer. If serum treatment is to be carried out in all cases due to any 

 of the thirty or more serological types, the production of these se- 

 rums would be greatly simplified by employing small animals 

 rather than horses. It is also probable that the cost of producing 

 immune rabbit serum may be less than the cost of producing con- 

 centrated antipneumococcic horse serum. Preliminary clinical 

 trials with antipneumococcic rabbit serum have been sufficiently 

 encouraging to invite further study of this seemingly important 

 advance in the serum treatment of lobar pneumonia.* 



The details of the mechanism by which immune serum overcomes 

 pneumococcal infections are only partly known. When the immune 

 serum is type-specific and high in antibody content, the cocci are 

 clumped and possibly to some degree removed from the circulation 



* The foregoing statements are the conclusions of Horsfall, Goodner, and 

 MacLeod.659 



