208 THE INFECTIOUS DISEASES. 



wholly lose this virulence under artificial cultivation. On the other hand, cultures of 

 streptococci which have largely lost virulence under artificial cultivation, or whose 

 initial virulence was slight, may experience a great exaltation of virulence by a long 

 succession of inoculations from animal to animal. 1 



The metabolic products formed by virulent streptococci growing in nutrient 

 broth, when freed from the germs by filtration, have been found to induce in animals 

 the symptoms of toxaemia. The results of preliminary experiments on immunization 

 with these toxic products of S. pyogenes and the use of the blood serum of the immune 

 animal for therapeutic purposes appear to be promising. But the practical value of 

 the so-called streptococcus antitoxin is at this date not fully determined. 



ERYSIPELAS. 



Erysipelas is a diffuse inflammation of the skin and subcutaneous 

 tissue which tends to spread, and is characterized locally by swelling of 

 the tissue and a bright-red color of the integument. It is usually accoin- 



FIG. 98. ERYSIPELAS OF THE SKIX. 

 Showing streptococci in the lymph spaces. 



panied by constitutional disturbances, the most marked of which is fever. 

 The morphological changes at the seat of lesion, as we see them after 

 death, vary considerably in different cases and in different stages of the 

 disease. The redness of the skin usually disappears after death. But 

 the tissues may be swollen by the accumulation of serous fluid. This 

 fluid may be nearly transparent, or turbid from admixture with pus cells 

 (Fig. 98) . Pus cells may infiltrate the tissues either sparsely or in dense 

 masses. Fibrin may be present, abscesses may form. Sometimes vesi- 

 cles or scabs are found on the surface, or the affected region may become 

 gangrenous. Aside from the local lesions, there may be toxaemia marked 

 by petechice in the serous membranes, swelling of the spleen, focal necro- 

 ses, and albuminous degeneration in the kidneys and liver. 



The most common excitant of erysipelas is Streptococcus pyogenes. 8 



1 For bibliography of streptococcus consult the article by v. Lingelsheim, in Kolle 

 and Wassermann's "Handbuch der Mikroorganismen," Bd. ii., p. 303; for a study of 

 the action of streptococcus toxin on various parts of the body see llomen and others, 

 Ziegler's ''Beitrage," Bd. xxv., p. 159, 1899. 



'* In the early days of modern bacteriology the "chain " coccus which was discov- 

 ered in the exudate of erysipelas was thought to bear a peculiar relationship to this 

 clinical form of phlegmonous inflammation and was called by Fehleisen Streptococcus 

 erysipelatis, but it has now been definitely identified with the S. pyogenes. 



