220 



SCIENCE. 



[N. S. Vol. XXIII. No. 580. 



so as to permit free passage of steam to 

 and from the gauge. The stoppers of 

 flasks are further protected by means of 

 small beakers, inverted over the necks of 

 the flasks, during sterilization. Test tubes 

 are protected, in a similar way, by small 

 pans of thinnest sheet copper, made to fit 

 -over the wire baskets containing them. 



The Production of Acid and Alkali by 

 Bacteria: E. 0. Jordan, University of 

 Chicago. 



Since Theobald Smith's work in 1895 it 

 has been known that the acid reaction that 

 develops in the broth cultures of many 

 bacteria is produced by the action of the 

 bacteria upon muscle-sugar. It has not 

 been definitely recognized, however, that 

 there are other substances besides sugar in 

 the ordinary nutrient media which, under 

 the influence of bacterial activity, lead to 

 the production of a strongly acid reaction. 

 One prominent text-book, indeed, afSrms 

 that 'the formation of free acid is pos- 

 sible only upon nutrient media containing 

 sugar.' As a matter of fact, I have found 

 the liquefaction of gelatin by bacteria or 

 their sterile enzymes always gives rise to a 

 marked acid reaction which may amount 

 to as much as nine per cent. (B. suhtilis) 

 on the acid side of the phenolphthalein 

 neutral point. A reaction of plus four per 

 cent, is quite common in ciiltures of lique- 

 fying species. This is not surprising when 

 it is remembered that substances like glyco- 

 eoll and the amino-acids are conspicuous 

 among the digestion products of gelatin. 

 The simultaneous production of ammonia 

 by bacteria tends to diminish the acidity 

 of liqiiefied cultures, in some cases {e. g., 

 B. pyocyaneus at 20°) the acidity being 

 nearly or quite overcome. The acidity is 

 not confined to the liquefied area, but, as 

 might be supposed, diffuses throughout the 

 medium, altering the reaction of the gelatin 

 at quite distant po'iiits. In nutrient agar, 



on the other hand, the diffusion of alkaline 

 products alters the reaction of the medium 

 in the opposite direction. A standard re- 

 action for culture media, therefore, is valid 

 only as an initial reaction. Gelatin and 

 agar, inoculated with liquefying species, 

 begin to diverge from the start and in a 

 short time may become totally different. 

 Bacteria make their own reaction in broth, 

 gelatin and agar and, useful as a standard 

 reaction may be, it has distinct limitations. 

 Some writers have attempted to establish 

 a fundamental distinction between acid and 

 alkali production by bacteria. Thus Got- 

 schlich in KoUe and Wassermann's 'Hand- 

 bueh, ' 1, p. 100, expresses himself as fol- 

 lows : " In general it may be said that acid 

 production always depends upon a split- 

 ting of sugar (or similar substances, like 

 glycerine, etc.) ; while alkali formation is 

 a synthetic process and stands in intimate 

 causal relation with the growth and in- 

 crease of bacteria." Such a view would 

 seem to be eminently artificial, since the 

 ammonia to which an alkaline reaction is 

 due is as truly a decomposition product 

 of nitrogenous bodies as the amino-acids 

 formed in the digestion of gelatin of the 

 lactic acid in the fermentation of sugar. 

 Both processes go on simultaneously, and 

 the reaction of a culture medium in which 

 bacteria are growing depends not only on 

 the ability of the species to attack certain 

 food siibstances, and on the chemical con- 

 stitution of those food substances them- 

 selves, but also on the precise period of 

 growth at which the reaction is tested. 



Experiments on the Staining Properties of 

 Bacteria, with Special Reference to the 

 Gram Method: D. H. Bergey, University 

 of Pennsylvania. 



Careful search in text-books fails to re- 

 veal definite information as to the factors 

 concerned in the Gram method of staining. 

 There is even confusion in different text- 



