82 BACTERIOLOGY. 



The toxins of the Bacillus pestis are both endo- 

 and extra- cellular. It is possible to immunize animals 

 and, in their blood, substances that will agglutinate 

 the bacilli are found. They may be used in the diag- 

 nosis of the disease. In human beings an immunity 

 develops after one attack. A protective serum' has 

 been used against the disease, and is said to reduce the 

 mortality rate 20 to 25 per cent. 



THE BACILLUS PYOCYANEUS. 



The discharges from open wounds occasionally 

 have a green color, the cause of the color in these cases 

 being due to a pigment formed by the Bacillus pyo- 

 cyaneus. It is a short, actively motile rod, having a 

 tendency to form chains in fluid media. It can be 

 readily cultivated in the presence of oxygen, and is 

 easily identified because it stains the media upon which 

 it grows a brilliant green. It forms no spores. 



This organism possesses no great virulence, and 

 may live without producing injury on the skin, and in 

 the respiratory and intestinal tracts of animals and 

 man. It may, however, be the cause of serious infec- 

 tions, but in such cases it is due to greatly lowered 

 resistance in the patient rather than to the virulence of 

 the bacillus. It may be the cause of otitis media and 

 diarrhea and gastroenteritis in children. Cases of 

 general sepsis, liver abscess, and pericarditis have been 

 attributed to it. 



The pigment produced is of two kinds; one is 



