1 72 BACILLUS SUBTILIS AND ITS CONGENERS. 



sweet odour. At a somewhat earlier stage, before the surface is 

 entirely covered with skin, the liquid (which on this account 

 becomes turbid) swarms with numerous actively motile rods. 

 Formerly, with the . defective instruments at command, only a 

 single cilium could be discerned on each of the terminal poles (see 

 A, Fig. 40), but subsequent researches established the fact that 

 Bacillus subtilis, like many other species, is 

 richly endowed with cilia, as may be seen from 

 Fig. 41, which is reproduced from a photo- 

 graph. The development of the motile rods 

 into the multicellular chains constituting the 

 skin must be regarded as a transition to the 

 quiescent stage. The formation of this wrinkled 

 cover first becomes noticeable when the nutrient 

 medium is in an advanced state of decomposi- 

 tion. In most of the cells composing the chain 

 FIG. 4i.-Bacmus subtilis. there wiu then be found a firnij brilliant endo- 

 cnia staining. gpore ^ -pig, 40), producing an uncommonly 

 beautiful and rema rkable appearance. The 

 walls of the mother-cell swell up, the chain is 

 dissolved, and the endospores thereby liberated. Some facts in- 

 dicative of their power to resist adverse influences have been given 

 in a previous section ( 53). The spore membrane is capable of 

 swelling up, so that when the spores are placed in water, each of 

 them soon appears to be surrounded by a dull halo the swollen 

 external layer of the membrane. 



109. Influence of the Mode of Nutrition on the 

 Form of Growth. 



This factor was exhaustively described, for the bacillus in 

 question, by HANS BUCHNER (IV.). A few of the forms of growth 

 observed are shown in Fig. 42. By employing a faintly alkaline 

 5 per cent, solution of meat extract, rods (as at ia) are obtained, 

 0.5 ju, broad and 6-10 /x long. If a neutral solution of 5 per cent, 

 of sugar and o.i per cent, of meat extract be taken, then the forms 

 shown in 2 a appear, viz., short rods 0.8 /u, broad and only 4-6 //, 

 long. Finally, in an infusion prepared from hay in which woody 

 stems predominate, the cells (3) have a length of 12 /x and a 

 breadth of i.o /x. Under all the above conditions reproduction 

 goes on with vigour, the fission being very rapid. The new parti- 

 tion walls formed during the operation are at first so thin and so 

 faintly refractive as to escape the eye in the case of unstained pre- 

 parations. If, however, a solution of iodine be added, then the 

 apparently uniform long cells are seen to be divided into short 

 cells in the manner diagrammatically sketched at b and c in the 

 Fig. All these shapes belong to the cycle of normal forms of 

 growth, of strong vitality, and capable of reproduction. When, 



