86 SOLID CULTIVATION MEDIA. 



antly on the surface of the jelly, where it is found heaped up around 

 the point of inoculation, with a slightly elevated free surface of a 

 bright rose pink colour. It also grows downwards into the jelly, fol- 

 lowing the line of inoculation, and presenting the appearance of a 

 smooth sharp-pointed spike, of a dull grey pink colour. It does not 

 cause liquefaction of the jelly, and after developing to the extent de- 

 picted in Fig. 39, it ceases to grow, and passes into a stage of quies- 

 cence ; but it retains the power of further propagation, if transplanted, 

 for an indefinite period. 



Amongst the pathogenetic organisms which flourish in this medium 

 is that which gives rise to acute osteo-myelitis (see Fig. 38), first fully 

 described by Becker. It grows chiefly within the jelly, following the 

 track of the inoculating wire, along which a series of very fine nodules 

 is produced. These nodules have a faint yellow tinge, and are seen 

 to be perfectly smooth in their outlines when looked at with a magni- 

 fying glass. On the sixth and seventh day after inoculation, liquefac- 

 tion of the jelly commences, producing first a funnel-shaped depres- 

 sion full of liquefied jelly, and gradually extending, first to the 

 periphery of the test-tube, and then downwards, till the whole of its 

 contents become liquid. An amorphous deposit of a yellow colour is 

 found at the bottom of the test-tube, and the whole of the super- 

 jacent liquid is slightly tinged with the same colour. Re-inoculations 

 of culture material must be frequently repeated in the case of this 

 organism, as its vitality is lost soon after it has exhausted all the 

 available nourishment of one of the tubes of jelly, and it becomes 

 quite inert unless it is speedily supplied with fresh pabulum. 



When an observer is acquainted with the typical form of growth 

 which a species exhibits in Koch's jelly, he has no difficulty in de- 

 tecting the presence of impurities should they gain access to the con- 

 tents of the tube. Modifications are at once apparent in the type of 

 the growth which takes place, or an organism with quite distinctive 

 characteristics may be seen growing alongside that already cultivated ; 

 an instance of this is supplied by Fig. 43, in which a cultivation of 

 Bacillus anthracis is figured in which this accident has occurred. The 

 upper part of the jelly has liquefied in the usual way, but at a lower 

 part of the test-tube is an opaque spherical mass, seen with a pocket 

 lens to consist of a central nodule, with delicate silky fibrils stretching 



