204 



Profs. P. F. Frankland and Marshall Ward. 



Again, as is well known, there are several forms which will not 

 grow on gelatine at all,* and there are others which grow so slowly 

 that they will not be counted in the estimations made by gelatine- 

 plate cultures, either because the colonies formed in the time are too 

 small to be seen, or because they succumb to dominant forms — for it 

 must never be forgotten that, among competing Schizomycetes, it is 

 especially the early forms which gain the advantage, as elsewhere in 

 nature. 



Finally, since the temperature has been shown to be such a deter- 

 mining factor in the growth and multiplication of bacteria, we may 

 be sure that this item affects these plate cultures also, and it is well 

 known that different numbers are obtained according to the tem- 

 perature of incubation, and with reference to this point it is especially 

 to be noted that the optimum temperatures for different bacteria 

 may differ considerably.t 



Taking all the facts into consideration, therefore, it is necessary to 

 regard the gelatine-plate method as an imperfect one at best. But if we 

 inquire whether there is a better one, we are bound to reply that there 

 is not, at any rate for general purposes ; but for special requirements 

 it is possible to devise several modified methods for the culture of par- 

 ticular forms, and this has been done in certain cases. 



§ III. The Vitality of Micro-Organisms in Water. 



It is now time to enter upon the special literature dealing with the 

 behaviour of selected forms of Schizomycetes in particular samples 

 of water, and we propose to treat this somewhat more in detail, and 

 in chronological order, so far as possible, because it bears directly 

 on the subject of our enquiry. J 



This invesigation followed as the natural corollary to the discovery 

 that some micro-organisms can multiply to a most extraordinary 

 extent in waters almost entirely destitute of organic matter, like 

 distilled water. The first recorded instance of such multiplication 



* Pome of these are of the highest importance in connexion -with the chemical 

 changes taking place in natural waters, e.g., the nitrifying organisms (Percy F. and 

 Grace C. Frankland, "The Nitrifying Process and its Specific Ferment," 'Phil. 

 Trans.,' 1890, B, p. 107 ; Winogradsky, ' Ann. de l'lnst. Pasteur,' 1890 and 1891 ; 

 Warington, ' Chem. Soc. Journ.,' 1891, p. 484). 



+ In this connexion it should be noted that the range of temperature for different 

 bacteria is much larger than is commonly assumed. There are species which 

 will grow at 0° C, and there are others which grow at temperatures as high as 

 50—70° C. See Fischer (" Bakterienwachsthum bei 0° C, &c," ' Centr. f. Bakt.,' 

 vol. 4, 1888, p. 89), Globig ('Zeitschr. f. Hyg.,' vol. 3, p. 294), Forster (' Centr. f. 

 Bakt.,' vol. 2, p. 337), Miquel ("Monogr. d'un Bacille vivant au-dela de 70° C," 

 'Ann. de Micrographie,' Annee I, Paris, 1888, pp. 4—10). 



X See Appendix C, p. 268- 



