APPEARANCES OF CULTURES 



369 



(requiring a small diaphragm for their definition), finely granular 

 in appearance, and with a very coarsely crenated and well- 

 defined margin. The deep colonies are usually spherical, some- 

 times lenticular in shape, and are smooth or finely granular on 

 the surface, and more opaque than the superficial colonies. In 

 cover-glass preparations, the bacilli are found to present the same 

 microscopic appearances as in preparations from solid organs, 

 except that there may be a greater number of the longer forms 

 which may almost be called filaments (Fig. 111). The same is 

 true of films made from young gelatin cultures. Sometimes the 

 diversity in the length of the 'bacilli is such as to throw doubt 

 on the purity of the cul- 

 ture. As a general rule, 

 in a young (twenty-four 

 or forty-eight hours old) 

 culture, grown at a uni- 

 form temperature, the 

 bacilli^ are plump, and 

 the protoplasm stains 

 uniformly. In old cul- 

 tures, or in cultures 

 which have been exposed 

 to changes of tempera- 

 ture, the protoplasm 

 stains only in parts ; 

 there may be an appear- 

 ance of irregular vacuola- 

 tion either at the centre 

 or at the ends of the 

 bacilli. 



Motility. In hanging- 

 drop preparations the bacilli are found to be actively motile. 

 The smaller forms have a darting or rolling motion, passing 

 quickly across the field, whilst some show rapid rotatory motion. 

 The filamentous forms have an undulating or serpentine motion, 

 and move more slowly. Hanging-drop preparations ought to 

 be made from agar or broth cultures not more than twenty-four 

 hours old. In older cultures the movements are less active. 



Flagella. On being stained by the appropriate methods 

 (vide p. Ill), the bacilli are seen to possess many long wavy 

 nagella which are attached all along the sides and to the ends 

 (Fig. 112). They are more numerous, longer, and more wavy 

 than those of the b. coli. 



Characters of Culture. Generally speaking, on artificial. 

 24 



FIG. 111. Typhoid bacilli, from a young 

 culture on agar, showing some filamentous 

 forms. 

 Stained with weak carbol-fuchsin. x 1000. 



