STREPTOCOCCUS PYOGENES 337 



long axis of the chain, adjacent cocci often show slight flattening of the 

 contiguous surfaces, forming, as it were, a series of diplococci arranged 

 end to end. As a general rule the streptococci pathogenic for man, 

 when grown upon favorable media, have a tendency to form chains 

 made up of at least eight or more individuals, while the more saprophy- 

 tic, less pathogenic varieties are apt to be united in shorter groups. 

 Upon this basis a rough morphological distinction has been made by v. 

 Lingelsheim, 1 who first employed the terms Streptococcus "longus" 

 and "brevis." A differentiation of this kind can hardly be re- 

 lied upon, however, since the length of chains is to some degree de- 

 pendent upon cultural and other environmental conditions. Species 

 which exhibit long and tortuous chains, when grown upon suitably 

 alkaline bouillon, or ascitic broth, may appear in short groups of three or 

 four, or even in the diplo form, when cultivated upon solid media or 

 unfavorable fluid media. Stained specimens often show swelling and 

 enlargement of individual cocci, giving the chains an irregularly beaded 

 appearance. These swollen individuals are probably to be interpreted as 

 involution forms and are seen with especial frequency in old cultures. 

 Streptococci do not form spores, are non-motile, and do not possess 

 flagella. There can be no doubt that certain species of true streptococci 

 may possess capsules, though these are not so regularly demonstrable 

 and are more delicately dependent upon cultural conditions than are the 

 capsules of the pneumococci. 2 The capsulated streptococci will be dis- 

 cussed more comprehensively in the section upon the differentiation of 

 pneumococcus from streptococcus (page 367). 



Streptococci are easily stained by the usual anilin dyes. Stained 

 by the method of Gram, tho, pyogenic streptococci are not decolorized 

 and invariably retain the gentian- violet. Certain species found in stools 

 and described as Gram-negative, are rare and are non-pathogenic. 

 Others of the "Streptococcus brevis" variety, and purely saprophytic, 

 may stain irregularly by the Gram method. 



Cultivation. The pyogenic streptococci are easily cultivated upon 

 all the richer artificial media. While meat extract-pepton media may 

 suffice for certain- strains, it is usually better to employ those 

 media which have the beef or veal* infusion for a basis. For the 

 cultivation of more delicate strains of streptococci, especially when 



IT;. Lingelsheim, " Aetiol. u. Therap. d. Streptok. Infek." Beit. z. Exp. Ther., 



Hft. 1, 1899. 



'Pasquale, Zieglers Beit., xii; Bardet, Ann. de 1'inst. Pasteur, 1887; Schottmiilter, 

 Munch, ined. Woch., xx, 1903; Hiss, Jour. Exp. Med., vi, 1905. 



