GROUP OF PYOGENIC COCCI. 
47 
a number of instances to milk infected by some person 
handling the milk. Acquired immunity following 
these infections, if it occurs at all, is of very short 
duration. In animals, however, it has been possible to 
produce an active immunity in horses and the serum 
of the animals so immunized can be used to produce 
passive immunity in human beings. 
The results obtained from the use of antistrepto¬ 
coccus serum have been successful in some instances 
but its action is uncertain. The difficulty lies in the 
fact that there exists a great many strains of strepto¬ 
cocci and unless the serum contains the protective 
substances for the particular strain causing the infec¬ 
tion no successful result can be expected. 
The Micrococcus tetragenus is a pus-forming 
organism of low-grade virulence. Its arrangement is 
peculiar, forming squares of four cocci. It is found 
frequently in the sputum and causes infection usually 
in combination with some other micro-organism. 
The gonococcus is the organism causing gonor¬ 
rhea. It is a diplococcus, always occurring in pairs 
with the surfaces facing one another flattened like two 
coffee-beans. It does not stain by Gram. In pus it is 
found almost always within the bodies of the leuco¬ 
cytes. It is very difficult to cultivate, as it does not 
grow on the ordinary culture media. By the 
diplococcus form, coffee-bean shape, situation within 
the leucocytes, and Gram negative stain, it is identi¬ 
fied by direct microscopic examination of pus. 
Infection with the gonococcus, or gonorrhea, is 
Micro¬ 
coccus 
tetrage. 
nus 
The gono¬ 
coccus 
