306 



MICROBIOLOGY 



dominate in numbers vary from 0.8 to 2.0 //, in breadth and 

 from 2 to 3 /x in length. Ward 2 found that, in old cultures 

 involution forms of considerable variation occurred. It pos- 

 .sesses a very pronounced capsule. Spores have not been de- 

 tected. It occurs usually 

 singly and more rarely in 

 short chains. Ward thought 

 that it possessed slight mo- 

 tility but he was unable to 

 demonstrate flagella. 



Staining. It stains readily 

 with the aniline dyes. With 

 carbol fuchsin it exhibits an 

 irregular arrangement of the 

 cellular protoplasm. This con- 

 dition is most conspicuous in 

 preparations made from bouil- 

 lon cultures. It is Gram posi- 

 tive. The capsule can be 

 demonstrated by the application of Welch's glacial acetic acid 

 method and by the Gram stain. 



Cultivation. It grows readily on the ordinary media in the 

 presence of air. It grows most readily at room temperature. 

 Agar. The growth appears in agar plate cultures in 24 

 liours after inoculation as circular grayish colonies 1 to 2 mm. 

 in diameter. Young colonies are opalescent and exhibit the 

 phenomenon of diffraction of light. Mature colonies may be 

 irregular in contour, flat, with sharply denned borders, and 

 grayish white in color. The growth is viscid. After several 

 weeks, when the culture medium has dried perceptibly, the 

 viscid character tends to' disappear, and the colony becomes 

 more pasty in consistency. In such old cultures, faint concen- 

 tric markings are visible near the border. On the surface of 

 slanted agar, the young growth is opalescent and usually con- 

 sists of numerous small confluent colonies. The condensation 

 2 Ward. Bulletin 165, Cornell University Agric. Exp. Station, 

 Ithaca, N. Y., 1899. 



Fig. 64. Bacterium subviscorum : 

 (a) in milk showing capsule, (b) 

 and (c) stained preparations 

 from cultures (Ward) 



