200 VETERINARY BACTERIOLOGY 



in various sugars. This seems to be helpful in determining the 

 origin of intestinal types in some cases. 



Pathogenesis. Unexplained differences and variations in 

 pathogenesis may be noted in the various strains which have 

 been studied. Virulence for a given species of animal may be 

 increased by passage through that species. 



Mechanism of Disease Production. Little more is known of the 

 mechanism of disease production with this organism than with the 

 staphylococci. Neither the hemolytic streptolysin nor the endo- 

 toxins, which have been described, seem adequately to explain its 

 pathogenesis. Changes are usually brought about in tissues 

 which are in more or less intimate contact with the organism. 

 No class of infections shows better the necessity of virulence of 

 an organism and lack of resistance on the part of the tissues in 

 order to bring about pathologic changes. 



Experimental Evidence of Pathogenesis. Inoculation experi- 

 ments of animals have duplicated practically every infection with 

 which this organism has been found associated in man and 

 animals. The causal relationship of the organism to many in- 

 fections has been abundantly demonstrated. All laboratory 

 animals may be infected with strains exhibiting sufficient 

 virulence. 



Disease and Lesions Produced. Streptococcus pyogenes is asso- 

 ciated as primary cause with a long list of affections in both man 

 and animals. As a secondary invader it is of great importance 

 in many other diseases. Mixed infections with Micrococcus 

 aureus and other organisms are common. Some of the more 

 important are worthy of note. 



Wound Infection and Suppuration. Streptococcus pyogenes is 

 not as common in surgical wounds and other traumata as the 

 Micrococcus aureus and M. albus. Karlinski, in 1890, examined 

 suppurative processes in man, animals, and birds, and found 

 that Streptococcus was present in about 22 per cent, of the cases 

 in man, 27 per cent, in lower animals, and 15 per cent, in birds. 

 Staphylococci were present in about 70 per cent., 54 per cent., 

 and 55 per cent, respectively. Lucet found Streptococci alone 

 in 9 cases, and associated with other organisms in 10 cases, out of 

 a total of 52 examinations of abscesses in cattle. Both Strcplo- 



