EXPERIMENTAL INOCULATION. 153 



Guinea-pigs are less susceptible ; sometimes only a local abscess with 

 a good deal of necrotic change results, sometimes, however, there is 

 also septicaemia. 



Experimental Inoculation. We shall consider chiefly 

 the staphylococcus pyogenes aureus and the streptococcus 

 pyogenes, as these have been most fully studied. 



It may be stated at the outset that the occurrence of 

 suppuration depends upon the number of organisms intro- 

 duced into the tissues, the number necessary varying not 

 only in different animals (e.g., suppuration being much more 

 easily produced in rabbits than in dogs) but also in different 

 parts of the same animal, a smaller number producing 

 suppuration in the anterior chamber of the eye, for example, 

 than in the peritoneum. The virulence of the organism 

 also may vary, and corresponding results may be produced. 

 Especially is this so in the case of the streptococcus pyogenes. 



The staphylococcus aureus, when injected subcntaneously in 

 suitable numbers, produces an acute local inflammation which 

 is followed by suppuration, in the manner described above. 

 The cocci multiply in the lymphatic spaces, and many are 

 found within leucocytes and also invading the capillary 

 walls. Wherever the condition is spreading the cocci are 

 present in the tissues at the margin, but after it has ceased 

 to spread they are practically confined to the pus. The 

 spread of the suppuration goes pari passu with the growth 

 of the cocci. When the suppuration has ceased to spread, 

 we find reaction on the part of the connective tissues in 

 the form of cellular proliferation and formation of new 

 capillaries, which lead to the formation of a granulation 

 tissue barrier. After this has been well formed the cocci 

 are found to diminish gradually in numbers and finally 

 they disappear. Intraperitoneal injection produces a sup- 

 purative peritonitis which may remain local, but which 

 usually spreads and kills the animal. 



Intravenous injection in rabbits, for example, produces 

 interesting results which vary according to the quantity 

 used. If a considerable quantity be injected, the animal 

 may die in twenty -four hours of a general septicaemia, 



