222 EVOLUTION AND DISEASE, 



of the specific bacteria ; some are more virulent, others 

 are slower in attaining maturity, or are more irritating 

 to the tissues. 



This view of the nature of inflammation is of some 

 importance, for it shows that the process may take place 

 in any compound cellular organism, and it certainly takes 

 place in plants ; for example, the galls on leaves due 

 to the deposition of eggs in their interstices by insects ; 

 each insect producing in this way a different variety of 

 gall, so that one leaf may present at the same time 

 several varieties of galls. 



The modification of the inflammatory process accord- 

 ing to the nature of the irritant is of interest in its 

 bearing on the evolution of specific diseases. The course 

 of a specific contagious disease, whether due to bacterial 

 infection or to noxious agents produced by bacteria, pre- 

 sents well-marked stages. The first is known as the 

 incubation stage, which may vary from a few hours to 

 days, or even weeks : this is succeeded by a stage of 

 eruption, in which the body presents manifestations of 

 the presence of noxious particles, such as a rash in small- 

 pox, scarlet fever, measles, and the like, or a sore limited 

 to a small area of the body, as in glanders, anthrax, 

 syphilis, &c. 



These outward signs are accompanied by fever and 

 general disturbance, marking the maturation of the 

 poison in the organism. After a variable period the signs 

 gradually subside, or terminate the life of the individual, 

 or the bacteria continuing to thrive in the organism may, 

 with the maturation of successive generations, produce 

 periodical disturbance at intervals of several hours, or 



