MECHANISM OF INFECTION AND IMMUNITY 233 



consigns thousands to the grave, consigns tens of thousands to a 

 worse fate to hopeless poverty, for fever spares the children and 

 cuts off the parents, leaving the wretched offspring to fill the future 

 ranks of prostitution, mendicancy and crime." Creighton says : 



The best illustrations of the greater severity and fatality of typhus among 

 the well to do come from Ireland in times of famine, and will be found in 

 another chapter. But it may be said here, so that this point in the natural 

 history of typhus may not be suspected of exaggeration, that the enormously 

 greater fatality of typhus (of course, in a smaller number of cases) among 

 the richer classes of the Irish families, who had exposed themselves in the 

 work of administration, of justice, or of charity, rests on the unimpeachable 

 authority of such men as Graves, and on the concurrent evidence of many. 



In the active stage of disease due to bacterial invasion of the body, 

 the body cells supply the ferment, the bacterial cells constitute the 

 substrate; the process is essentially destructive and analytic; complex 

 cellular proteins are split into simple soluble bodies ; the protein poison 

 is set free, exerts its deleterious effects on the body cells and disturbs 

 the health ; the evidence of infection rises to the plane of clinical obser- 

 vation; the symptoms of the disease become manifest and the contest 

 between bacterial and animal cells continues until one or the other 

 holds possession. 



It should not be understood that there is always a sharp line of 

 demarcation between the period of incubation and the appearance of 

 active disease. The bacterial growth may be extending into new parts 

 of the body coincidently with its destruction in other regions. 



Fever. All bacteria are capable of inducing fever, and this is a 

 most constant accompaniment of infection. Fever is not directly due 

 to the growth of bacteria in the body. It is not in evidence during 

 the period of incubation when bacterial growth is most abundant. The 

 early progress of tuberculosis is without fever, because at this time 

 the number of bacilli in the body is few and most of these are living. 

 It is not until the body becomes sensitized against the invading organ- 

 ism and begins to digest and destroy it that fever makes its appear- 

 ance. The face may be covered with acne pustules, each of which con- 

 tains streptococci, and still there is no elevation of temperature, 

 because the cocci are not reached and digested by the bacteriolytic 

 enzymes of the blood and lymph. The fever of infection results from 

 the parenteral digestion of the bacterial proteins. 



