180 INFECTIVE DISEASES. 



greyish-white, translucent dots or droplets, which can be more easily 

 recognised with the aid of a pocket lens (Fig. 87). According to 

 the number of organisms sown on the jelly, the dots or colonies 

 may be completely isolated, or form a more or less continuous 

 film. The film by reflected light has an iridescent appearance like 

 mother-of-pearl, but has a bluish or bluish-grey tint by transmitted 

 light, and with a pocket lens appears distinctly brownish. The 

 gelatine is not liquefied, and even after several weeks the cultivation 

 is limited to the inoculated area, and the individual colonies are, as 

 a rule, not larger than pins' heads. In gelatine-cultivations of the 

 same age, but kept in the incubator at 18° C, the colonies get 

 ii^regular in form, especially at the margin of the film, and give the 

 growth an ai'borescent, fringed, or serrated appearance. Cultivated 

 on the oblique surface of nutrient agar-agar at 37° 0. the growth is 

 very similar, forming a film composed of minute white colonies 

 hke grains of sand ; but the film appears less transparent, is 

 • whiter, and the colonies have a greater tendency to geit irregular 

 in form. If inoculated with one tracing of the needle the growth 

 is scanty, but tends to get thicker in the centre than towards the 

 margins, which may have a terraced appearance. Inoculated in 

 the depth of gelatine, there appears after a day or two at 18° 0. a 

 thread-hke growth along the track of the inoculating needle. This 

 delicate growth is found on examination with a pocket lens to consist 

 of a linear series of extremely minute granules. In a few days' 

 more, the beads or granules become more marked, but even after 

 weeks, the cultivation only appears like a string of minute, white, 

 compact, globular masses or grains. In broth at 37° C. the cocci in 

 twenty-four hours create a turbidity, and gradually develop beauti- 

 ful chains varying in length according to the age of the cultivations. 

 Even in forty-eight hours there may be chains of eight, ten, twenty, 

 or a hundred elements. After a few days the growth settles down 

 at the bottom of the tube in the form of a white deposit, while the 

 supernatant liquid becomes again clear. 



Inoculated subcutaneously in the ear of rabbits, they produce in 

 two days an infiammatory thickening with erysipelatous redness, 

 or sometimes suppuration. 



They may occur in vaccine lymph, as the result of con- 

 tamination, and Pfeiffer suggested that before calf lymph is 

 employed for vaccination it should be tested on a rabbit's ear. 

 If in two days no rash has been produced, the possibility of the 

 presence in the lymph of Streptococcus pyogenes or erysipelatis 

 is excluded. 



