5 



of groups which the Americans term, collectively, " Type II 

 "(atypical)." These have been investigated by Stillman.* They 

 are related to Type II, because they are agglutinated by concen- 

 trated Type II serum, though not by the diluted serum, i.e., 

 they " possess partial antigenic characters common to the 

 " Type II pneumococcus." They are distinguished from typical 

 II "by a diversity of relations among themselves, and by a 

 " lack of the reversibility of their immune reactions with the type 

 " organism." Stillman examined 204 " atypical II " strains and 

 classified them into 12 distinct groups, on the basis of specific 

 agglutination in monovalent rabbit sera. He reported that, 

 out of 458 strains obtained from lobar pneumonias at the Rocke- 

 feller Institute in three years, 52 (11 per cent.) were " atypical II." 

 These " atypical " groups are not limited to cases of disease. 

 According to Stillman, they occur in 18*3 per cent, of normal 

 mouths. The next type, Type III or Pneumococcus mucosus, 

 possesses distinctive characters and is of common occurrence 

 in normal mouths. It accounted for 13 per cent, of the Rockefeller 

 series of lobar pneumonias published in 1917. 



So far, then, the Americans have made out fifteen serological 

 groups of pneumococci. There remain a large number of strains 

 which they have not been able to place in any comprehensive 

 system of groups, owing to the great diversity of their serological 

 reactions ; they have shown, however, that they do not belong 

 to any of the above 15 groups. This heterogeneous collection 

 they term " Type IV." This " Type " is very common in the 

 normal mouth. It accounted for 20-3 per cent, of the last 

 mentioned Rockefeller series of pneumonias. 



With reference to the relation of type to virulence, the same 

 Rockefeller report gives the following figures, which refer to 

 100 cases of lobar pneumonia not treated with serum. 



Type of pneumococcus. 



Incidence 

 per cent. 



Mortality 

 per cent. 



I. - 33 25 



II. - - 31 32 



III. - 12 45 



IV. ------ 24 16 



As regards serum therapy, they have produced a horse serum 

 which is useful in the treatment of pneumonia due to infection 

 with Type I, but they have not succeeded in obtaining a serum 

 which could be used for infections due to Types II or III or 

 the miscellaneous " Type IV." Evidence as to the value of 

 Type I serum has recently been given by Cole.f In 195 cases 

 treated with this serum at the Rockefeller Institute there were 

 only 1 8 deaths (9-2 per cent.). He has collected from the literature 

 records of 300 additional cases treated with the serum and finds 



* Journ. Exper. Med., XXIX, p. 351, 1919. 

 f Journ. Am. Med. Ass., Jan. 8th, 1921, p. 111. 

 x 17080 A 3 



