192 TEXT-BOOK OF BACTERIOLOGY. 



to a considerable extent. The appearance of well-isolated colonies 

 is then very characteristic. Balls as large as a hemp-seed are formed, 

 which shine in varying- gray tints, showing a peculiar star-like ar- 

 rangement in their interior, and being generally surrounded with 

 numerous sharp prickle-like spurs. Under the microscope, one 

 sees even with a low power a brisk motion in the liquefied portion, 

 and sees the irregular, fringe-like border of the colony still more 

 distinctly. 



In the interior of the liquid balls, small bubbles of gas soon 

 make their appearance, gradually grow larger, and at last even 

 unite with each other. Hand in hand with this goes another phe- 

 nomenon. While at first the growth was strictly confined to the 

 lower two-thirds of the gelatin, and the upper portion, to a depth of 

 several centimetres, remained quite barren, the culture now extends 

 upward. The solid covering at the top of the gelatin becomes 

 thinner and thinner, till only a few millimetres remain. The cause 

 of this is that the gaseous excretions of the bacillus expel the air 

 more and more, and with it the oxygen contained in the upper layer 

 of the gelatin, and the bacterium thus with its own products paves 

 the way for the conquest of new territory. 



All these things may be observed exceedingly well in the puncture 

 cultivation in gelatin with much grape-sugar. For a few days the 

 development takes place only in the deeper layers. The neighbor- 

 hood of the puncture is rapidly liquefied, the deeper the more com- 

 pletely. Numerous thorn-like processes push out into the still solid 

 portion, and the culture at this stage looks, as Liideritz says, like 

 a hairy caterpillar. As time passes on, the caterpillar (the culture) 

 creeps higher up, so that at length the entire gelatin is liquefied 

 from bottom to top, and the test-tube filled with a grayish- white 

 viscid mass, consisting of zoogloea of the bacilli. If we insert a 

 stout platinum needle into the culture and stir it up, great quan- 

 tities of gas-bubbles rise, and the liquor fairly sparkles. 



The gases which escape have a very unpleasant odor, reminding 

 one of rotten cheese and onions combined. Nothing is as yet known 

 with regard to the nature of these gases. 



In grape-sugar agar the growth is also rapid, the food medium 

 is usually burst open in numerous places Toy the great development 

 of gas, and occasionally it is even forced out of the test-tube along 

 with the pledget of cotton- wool. 



This bacillus thrives at ordinary temperature and in the incuba- 

 tor. It forms spores at ordinary room- temperature. Gelatin cul- 

 tures, therefore, retain their vitality for months and can be trans- 

 planted to a fresh food medium. 



