INFECTION ^ 



one of the three great groups of microscopic hfe, namely, bac- 

 teria, higher fungi, or protozoa. It is customary and convenient, 

 if not altogether logical, to limit the term microorganism to these 

 forms excluding altogether the entozoa and other animal para- 

 sites most of which are not microscopic in size. 



A diseased condition produced by substances not capable of 

 reproducing themselves as, for example, organic or inorganic 

 chemical compounds, is an intoxicative process. In an infection, 

 the immediate cause of the symptoms and morbid changes in 

 the tissues is an intoxication due to the action of the metabolic 

 products (toxins) of the invading microorganisms. The the- 

 ories of their mechanical interference with the normal functions 

 of the body or that they absorb the nutriment thus depriving 

 the tissues of necessary food wait for demonstration. The re- 

 sults of infection vary in their manifestations. If the invading 

 organisms remain at the point of entrance and produce local 

 tissue changes, the condition is spoken of as a wound mfedion ; 

 if the invading bacteria become widely distributed in the cir- 

 culation and tissues, the condition is known as septicaemia ; if 

 the infecting bacteria remain at the point of entrance, multiply 

 there elaborating a toxin which is absorbed and which causes 

 symptoms and possibly death, the condition is a toxaemia; 

 if the invading organism happens to be that of a specific dis- 

 ease, such as the bacterium of anthrax, giving rise to a defin- 

 ite series of symptoms and lesions, the affection is designated 

 a specific, infectious disease. Through the agency of metas- 

 tasis, invading microorganisms may be carried from the point 

 of introduction to other parts of the body where they may be- 

 come localized, multiply and give rise to any one of many 

 forms of lesions. It may happen that the point of entrance is 

 so obscure that the resulting morbid changes are not easily 

 traced to an external infection. There are many illustrations 

 of this in comparative pathology such, for example, as suppur- 

 ative cellulitis. For convenience in discussion, infections may 

 be divided into the two clinical groups, namely, wound infec- 

 tions and specific infectious diseases although in certain in- 

 stances they cannot be separated. 



