INFECTION 171 



CHAPTER V 



INFECTION VEGETABLE AND ANIMAL PARASITES THE 

 INFECTIVE PROCESS ANTI-BODIES ANTI-SERA AND 

 ANTITOXINS IMMUNITY 



Infection 



BY the term INFECTION is meant the invasion of the 

 living tissues by living micro-organisms which grow and 

 multiply at the expense of the host, and which may be 

 either animal or vegetable in nature. A disease produced 

 by the growth and multiplication of micro-organisms is 

 termed an infective disease, and is transmissible in most 

 instances by inoculation. If the micro-organisms are 

 from time to time discharged from the body of the host, 

 either with the excreta, secretions, desquamated particles, 

 or in some other way, the disease becomes infectious or 

 contagious, according to the ease with which another 

 individual becomes infected, and the material which con- 

 veys the infection is often termed the contagion or the 

 virus, though the latter is also applied to the organism 

 itself. Thus, in scarlatina and smallpox the contagion is 

 very readily conveyed from person to person even for a 

 distance through the air, and these are infectious diseases. 

 Ringworm and syphilis, as a rule, require more or less 

 close contact for infection to take place, and these are, 

 therefore, contagious diseases ; while malaria is neither 

 infectious nor contagious, since persons in the neighbour- 

 hood do not directly contract the disease, though it can be 



