PYOGENIC BACTERIA. 383 



genie for rabbits only. The author named, as a result of extended and 

 carefully conducted comparative studies, arrives at the following 

 conclusions: 



" According to my observations, there are two great groups among the 

 streptococci. These cannot be distinguished one from the other in cultures 

 in highly albuminous media (pus, blood serum), but present constant dif- 

 ferences when cultivated in bouillon. The decisive characteristics in this 

 medium are : macroscopic, the cloudiness of the medium ; microscopic, the 

 length of the chains. The two groups are with difficulty distinguished in 

 agar cultures ; more easily in gelatin, in which the streptococcus which 

 forms short chains causes a slight liquefaction, while the Streptococcus 

 longus does not. Upon potato Streptococcus brevis alone shows a visible 

 growth. . . . We see here a group of streptococci which we separate from 

 the others, because of their microscopic and cultural differences, under the 

 name of Streptococcus brevis, which is also distinguished by having no 

 pathogenic action upon the animals usually experimented upon. We 

 recognize, on the other hand, the streptococci which we have grouped to- 

 gether as Streptococcus longus as all pathogenic and about in equal degree 

 for a certain species of animal (rabbits) ; but by experiments upon other 

 species (mice) we arrive at the conclusion that there must also be differences 

 between these streptococci. It appears that the streptococci which are dis- 

 tinguished by their high degree of pathogenic power upon mice are also 

 those which are distinguished in bouillon cultures by the formation of con- 

 glomerate masses. We find among these also one which is distinguished 

 by especial virulence for mice, and that this one is distinguished in cultures 

 by its scanty growth upon ox serum." 



The more recent researches of Knorr (1893), and of Waldvogel 

 (1894), indicate that the classification of the streptococci proposed by 

 von Lingelsheim has no great value, and show that marked changes 

 in biological characters and in pathogenic power may result from 

 cultivation in special media, or from successive inoculations into 

 animals. 



Morphology. Spherical cocci, from 0.4 // to 1> in diameter, but 

 varying considerably in dimensions in different cultures, and even 

 in a single chain. Multiply by binary division, 

 in one direction only, forming chains, in which 

 the elements are commonly associated in pairs. 

 Under certain circumstances, instead of form- 

 ing chains, a culture may contain only, or 



chiefly, diplococci : but usually chains contain- 



* 

 ing from four to twenty or more elements are 



formed, and these are frequently associated 



in tangled masses. Occasionally one or more 



cells in a chain greatly exceed their fellows in 



size, and some bacteriologists suppose that FIG. 82. PUS containing 



these cells serve as reproductive spores arthro- (jS^ 00 



spores but this has not been definitely proven. 



Stains readily with the aniline colors and by Gram's method. 



