132 HACII.I.rs srBTIMS AM) ITS (OMiKNKRS 



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

 and Jliir'illiis Njibtilis by Cohn. To obtain them with certainty the following 

 process, known as the heat method, which was devised by ROBERTS (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 0., 

 the usually somewhat acid liquid being afterwards poured off (without 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 limit'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 C. 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 zoogloea. 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 sublUis by Brefeld is not identical with that of the 

 same name described by Prazmowski, 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 tip 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 command, only a single cilium could 

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

 ., iiiu- -ui.tiiis. 40), .but subsequent researches established the fact 

 < ilia staining. that /Irrri/litfi ftnbtilit*, like many other species, is richly 



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

 vhich is reproduced from -t photograph. The de- 

 velopment of the motile rods into the multicellular 

 oonfltitntiog the skin mtuM !> regarded .-is a transition to the quiescent 

 Stage. Tin* formation of iliis wrinkled c<>\<-r lir>t becomes imt irealile when the 

 nutrient medium is in an adv;in< . -d Btttto >!' decomposition. In most of the cells 

 e<>nipo-in;r the chain there will then l>e found a firm, brilliant endospore 

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



