i 32 BACILLUS SUBTILIS AND ITS CONGENERS 



exclusively in the form of short rods, and were named Vibrio subtilis by Ehrenberg 

 and Bacillus subtilis by Cohn. To obtain them with certainty the following 

 process, known as the heat method, which was devised by EGBERTS (I.), and 

 already referred to in 53, is employed: Dry hay is chopped up fine, 

 suffused with a little water, and then left to stand four hours, at about 36 C., 

 the usually somewhat acid liquid being afterwards poured oft' (ivithout filtering), 

 exactly neutralised, and diluted until it shows a density of 1.004. This liquid is 

 then boiled gently for an hour over the sand-bath in a flask plugged with cotton- 

 wool. Since the number of heat-resisting spores present on the hay is fre- 

 quently but small, sufficient hay and water are taken at the outset to yield at 

 least half a litre after an hour's boiling, which quantity will be sure to contain 

 some living germs. The flask is removed from the sand-bath, left to cool down 

 to the temperature of the hand, and then placed in the incubator, the tempera- 

 ture of which is regulated to about 36 0. during the ensuing twenty-four hours. 

 At the end of this time there will have appeared on the surface of the infusion 

 a thin skin, which subsequently thickens and develops to a typical zooglcea. A 

 little of this, examined under the microscope, will present the appearance shown 

 at G in Fig. 40, viz., a number of closely adjacent rows of short rods. 



108. Morphology of Bacillus subtilis. 



That, by the aid of Roberts' method, pure cultures (in the present acceptance 

 of the term) cannot be obtained, need hardly be insisted upon, all that is produced 

 being a culture of heat-resisting bacteria ; hence the "hay bacillus" prepared in 

 this way by different observers will vary. Really pure cultures may, however, 

 be obtained therefrom by modern methods of pure cultivation. The organism 

 examined and styled Bacillus subtilis by Brefeld is not identical with that of the 

 same name described by Prazmovvski, though allied thereto, and indeed so closely 

 that the physiologically important phenomena of spore- germination are alike in 

 both kinds. This circumstance has already been fully noticed in 58, and the 

 reader is therefore referred thereto. A few supplemental morphological facts 

 will now be added, the opportunity being also favourable for remarking that a 

 reliable culture of B. subtilis can be prepared by mixing crushed malt and rye in 

 a flask with about four times their volume of water, inserting a plug of cotton- 

 wool, boiling up the mixture, and then leaving it to 

 stand at 35-4o C. A thick, wrinkled skin will 

 rapidly develop on the surface of the liquid, and the 

 contents of the flask acquire a characteristic sickly- 

 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 tfommand, only a single cilium could 

 be discerned on each of the terminal poles (see A, Fig. 

 FIG. 41. Bacillus subtilis. 40), but subsequent researches established the fact 

 Cilia staining. that Bacillus subtilis, like many other species, is richly 



Magn. about 1500. (After endowed with cilia, as may be seen from Fig. 41, 

 A. Fischer.) which is reproduced from a photograph. The de- 



velopment 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 decomposition. In most of the cells 

 composing the chain there will then be found a firm, brilliant endospore 

 (D, Fig. 40) producing an uncommonly beautiful and remarkable appearance. 



