EXPERIMENTAL INOCULATION. 189 



stain readily with the common aniline dyes, occasionally showing plasmolytic 

 vacuolation ; they retain the stain in Gram's method. They are non-motile, 

 but Brownian movement is very active. No spores have been observed. 

 Growth occurs best at 37° C. on glycerin agar, whose reaction is 3 • o + to phe- 

 nol-phthaleine, on blood serum (Loffler's), and in bouillon, less frequently in 

 litmus milk. No growth is noticeable on potato, gelatin, or in Dunham's 

 medium. For successful- isolation from an acne node, glycerin agar or Lof- 

 fler's blood serum should be used, and the material from the nodule should 

 not be smeared over the surface but deposited in pieces about 2 c.mm. and 

 allowed to incubate a week or ten days, Then these small whitish masses 

 (which are in truth the bacilli themselves) will be found to have increased in 

 bulk and thrown out an extending grey zone of growth ; their consistency is 

 somewhat pultaceous, and they may be moved about en masse with the needle. 

 Old cultures take on a pink or light maroon colour, or sometimes a yellow-drab. 



In well-marked cases of the disease the blood of the patient will cause 

 agglutination of the bacilli in dilutions of 1-50, 1-60, and i-ioo. 



The organism is pathogenic to mice and guinea-pigs, either upon subcu- 

 taneous or intraperitoneal inoculation. 



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 suppu- 

 ration depends upon the number of organisms introduced into 

 the tissues, the number necessary varying not only in different 

 animals, 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 pro- 

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

 pyogenes. 



The staphylococcus aureus, when injected subciitaneously in 

 suitable numbers, produces an acute local inflammation which is 

 followed by suppuration, in the manner described above. The 

 spread of the suppuration goes pan passu with the growth of 

 the cocci. 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. In the latter 

 case reaction occurs on the part of the connective tissues in the 

 form of cellular prohferation and formation of new capillaries, 

 which lead to the formation of a granulation tissue barrier. If 

 a large dose is injected, the cocci may enter the blood stream in 

 sufficient numbers to cause secondary suppurative foci in inter- 

 nal organs {cf. intravenous injection). 



