84 PATHOGENIC BACTERIA. 



symptom-complex, made up of the symptoms and con- 

 ditions that usually present themselves; but wide devia- 

 tion from this type is to be expected. The deviations 

 are sometimes extraordinary and make the process at 

 first unrecognizable. Thus, pneumococcus infection 

 usually presents itself in the form of croupous, lobar 

 pneumonia, but occasionally appears as otitis media, 

 conjunctivitis, etc. Tuberculosis usually assumes the 

 pulmonary form, and appears as a disease whose chief 

 ravages affect that organ ; it is common as an affection 

 of the bones and joints, and not uncommon as lupus on 

 the skin. These three forms of the disease are so differ- 

 ent from one another that for many years their identity 

 was unsuspected. 



The Streptococcus pyogenes is usually associated with 

 severe local suppurative affections. It may be the cause 

 of erysipelas, of pseudomembranous sore throat, or of 

 rapidly fatal septicemia. Typhoid infection usually oc- 

 curs as clinical typhoid fever, but frequently makes its 

 appearance as local suppuration or as general septicemia. 



Conditions present in the animal body go far to modify 

 the course and appearances in disease; thus, should the 

 operations of a micro-organism be chiefly upon the tissues 

 iu their immediate vicinity, they usually operate at the 

 point of original entrance. The staphylococci usually 

 act locally at the seat of injury and infection, and bring 

 about suppuration. Their accidental entrance into the 

 lymphatic vessels with currents of lymph or enclosed in 

 phagocytes leads to lymphangitis and then to lymph- 

 adenitis. If they enter the circulation, the valves of the 

 heart may become a nidus for their operation, and endo- 

 carditis result; or metastatic abscesses may occur in con- 

 sequence of their transportation to and deposition in 

 remote tissues. 



Sometimes the micro-organism seems to find the con- 

 ditions ill-adapted to excessive development, and con- 

 sequently develops in a very limited — indeed, almost 

 insignificant — manner; yet because of soluble toxic met- 



