156 STREPTOCOCCIC INFECTION 



active for weeks, during which time there is a slowly progressive 

 emaciation. Intraperitoneal injections induce fatal peritonitis. Ani- 

 mals have been infected by feeding experiments. In such cases the 

 primary infection develops in the small intestine, causing an acute 

 enteritis and followed by systemic infection and death. Repeated 

 passage through animals rapidly increases the virulence and in this 

 way cultures have been obtained which kill rabbits in doses of 

 0.0000001 c.c. However, not all strains can be developed to this 

 extent. Association with certain other bacteria, such as the proteus 

 and colon bacillus, is favorable to an increase in virulence. The pres- 

 ence of bile seems to have a like effect. The condition of the animal 

 influences the rate of increase in virulence. Starvation, overexertion, 

 and other depressing influences render the animal more susceptible. 

 The same is true of the condition of the infected tissue. Extensive 

 bruises, lacerations, and other injuries favor the growth of the strepto- 

 coccus. When implanted on a mucous membrane already irritated 

 by chronic catarrh, scarlet fever, or diphtheria, this micro-organism 

 multiplies with unusual rapidity and develops marked virulence. Each 

 species of animal seems to have its own strain of streptococcus. The 

 bacterium accommodates itself to its peculiar host and thrives best 

 on that species. Those strains found on man are more pathogenic to 

 man than those found on other animals, and when the virulence of 

 any strain is increased by repeated passage through a certain animal, 

 it is more pathogenic to that than to other species. 



There is no tissue or organ of the human body immune to invasion 

 by this organism. When a virulent strain of the streptococcus finds its 

 way into the lymph vessels of the skin, erysipelas results. There is 

 marked migration of leukocytes to the infected area, which becomes 

 red and swollen and extends more or less rapidly. When experi- 

 mentally induced, the period of incubation varies from ten to sixty 

 hours. The injury done depends on the virulence of the infecting 

 strain and may be slight and superficial or it may be widely destructive 

 and fatal. The infection may extend to mucous surfaces, to internal 

 organs and to the brain and its membranes. A case of erysipelas does 

 not necessarily come from a preceding case of the same disease, for 

 the infection may be transferred from any pyemic or septic source 

 to the skin. Erysipelas may be acquired from puerperal fever or 



