86 
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 vaccine 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, Gram nega¬ 
tive, 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 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 
called pyocanin, soluble in chloroform; the other is a 
fluorescent pigment soluble in water. In old cultures 
a ferment-like substance is formed called pyocyanase, 
which has the property of dissolving some of the other 
forms of bacteria, It has been used to destroy diph- 
