THE GENUS DIPLOCOCCUS 113 



from which D. pneumonia produces acid, and that the 

 coagulation in presence of acid is markedly influenced by 

 heating the serum. Furthermore, it occurs, under certain 

 conditions, only at a certain optimum acidity, failing 

 when the serum is heated in the presence of a larger 

 amount of acid. 



The most important work upon this group of cocci, and 

 one of the best-planned campaigns ever executed in 

 bacteriological research, was the investigation carried out 

 by a number of independent observers under the auspices 

 of the Medical Commission for the Investigation of 

 Acute Respiratory Diseases, appointed on the initiation 

 of the Health Department of the City of New York. 

 That part of the work which bears upon the systematic 

 relationship of the diplococci and their allied forms may 

 be briefly summarized as follows: 



Park and Williams (1905), the first of the collaborators, 

 studied one hundred and forty strains of pneumococci. 

 They distinguished as typical those which occurred in 

 elongated pairs, showed capsules, coagulated inulin- 

 serum media, and produced a green coloration on blood - 

 agar plates. Among these, three variants were noticed, 

 one with small cells and narrow capsules, one with 

 large cells and broad capsules, and a zooglcea form, with 

 cells in chains of pairs. The latter is commonly known 

 as D. mucosus in America; but, as shown later, it should 

 rather bear the name D. involutus, Kurth. In addition, 

 two "atypical" forms were found, one resembling the 



