138 INFECTION 



5. The period of convalescence is now ushered in, during which the 

 host gradually overcomes the effects of disease and returns to health. 



During this entire time the emaciation and tissue exhaustion leave 

 the patient quite weak, and undue exertion, errors in diet, or reinfection 

 may lead to a relapse, or a reactivation of the disease. Certain sequelae 

 or morbid conditions may follow a disease, and are due to the same orig- 

 inal cause; e. g., in typhoid fever the development of cholecystitis; at 

 any time during the disease complications, or morbid conditions due 

 to some other microparasite, as the development of pneumonia during 

 the course of typhoid fever, may seriously jeopardize the life of the 

 patient. 



Grades of Infection. According to the manner in which a parasite 

 and its products act upon the cell of a host and the power of the host to 

 neutralize or overcome these the following various grades and types of 

 infection are encountered : 



(a) Malignant or fulminating infection, during which there is no 

 fever, but, on the contrary, a subnormal temperature, with rapid prostra- 

 tion of the patient and death within a brief period. The cells of the body 

 are overwhelmed and paralyzed by the toxic substances; metabolism 

 is arrested, and the heat centers are exhausted with the fall of the tem- 

 perature, an indication of the intense and overwhelming intoxication. 



(b) Acute infection, which is the ordinary type of an infectious disease 

 as previously described, and having a definite incubation period, prodro- 

 mal symptoms, fastigium, defervescence, and convalescence. 



(c) Chronic infection, or a prolonged process characterized by in- 

 sidious onset and symptoms of relatively mild or moderate severity, 

 and terminating either in death, after months or years, or in gradual 

 recovery. A chronic infection may be remittent, as may be observed 

 in the rheumatic group of disorders; during the remission with defer- 

 vescence the infecting bacterium is not totally destroyed, - and subse- 

 quently lights up, producing an acute exacerbation of the disease. 



In chronic infections it would appear that the parasites develop and 

 produce their toxins slowly, or that these are slowly and imperfectly 

 absorbed on account of the sluggish local circulation and the presence 

 of scar tissue. The body-cells become accustomed, as it were, to these 

 toxic products, and produce only sufficient antibodies to effect their imme- 

 diate neutralization. The bacteria themselves become distinctly resistant 

 to the action of the tissues and the defensive forces, and there is neither 

 the same degree of intoxication nor reaction as are seen in acute infec- 

 tions. Gradually, however, the body-cells become exhausted, and 



