THE RELATION OF BACTERIA TO DISEASE 49 



disease. Some authorities claim that pellagra is a germ 

 disease, but the weight of evidence appears against this 

 belief. On the other hand, acute articular rheumatism is 

 generally regarded as a germ disease, most bacteriologists 

 believing that the specific germ has not yet been identified. 



INFLAMMATION 



Inflammation is described as "a local reaction caused 

 by agents which have produced tissue injury." Among 

 the causes of inflammation we find blows, poisonous sub- 

 stances like snake venom, acids, or other irritant chemical 

 compounds, excessive heat or cold, and, finally, perhaps the 

 most important of all, bacteria. The degree of injury 

 produced depends on a number of factors. In the inflam- 

 mation due to bacteria it depends on the number of bac- 

 teria introduced, the virulence of the organisms, the length 

 of time they remain, and on the resistance of the infected 

 tissues. 



The first response on the part of the body consists in a 

 dilatation of the blood-vessels of the affected region and 

 a quickening of the blood flow. This quickening, how- 

 ever, is soon followed by a slowing of the blood-current, 

 and the passage through the wall of the blood-vessels 

 of blood-serum and white blood-corpuscles (leukocytes). 

 Sometimes the amount of blood-serum is small, but the 

 number of white blood-cells large; at other times the 

 reverse may be true. If the inflammation is severe, 

 red blood-cells also pass through the wall of the blood- 

 vessels. 



Let us see what takes place when some staphylococci 

 invade the deeper parts of the skin and give rise to a boil. 

 As soon as these germs have entered they act as an irritant 



4 



