202 



Profs. P. F. Frankland and Marshall Ward. 



from one germ, isolated at the time of infecting the gelatine, and 

 which developed in the medium during the period of culture. 



In the first place, the conclusion that each colony has sprung from 

 one germ is a mere assumption, and it is to be viewed with suspicion 

 at the outset. Cramer* showed that bacteria have a habit of sticking 

 together in the water, and several other observersf have shown that 

 this is a real danger in all bacteriological analyses, and that indi- 

 vidual colonies often result from the growth, &c, of not one, but 

 many agglomerated spores or segments. Many observers have 

 attempted to get over this difficulty by shaking the sowing in 

 distilled water, before infection. Wolffbiigel and Riedel suggest the 

 possibity that there are dangers connected with this method also, e.g., 

 removal of gases, oxidation, &c. It is even asserted that prolonged^ 

 mechanical shaking affects the growth of bacteria, but this concerns 

 the transit, &c, of cultures rather than the point under discussion. 



It has been suggested that the best method for ensuring separation 

 from one another of the bacteria would be to pass the water through 

 sterilised glass wool, as ElfVing did for spores of fungi ;§ only there 

 would be some loss. Thoroughly sterilised cotton wool, or even filter 

 paoers, may be used, but there is danger of washing traces of soluble 

 substances from these. 



The question as to whether the colonies result from a single germ 

 or from an agglomeration is, after all, not a matter of such grave 

 importance as might at first sight appear, for if the precaution be 

 taken, as it invariably should be, of violently agitating the sample of 

 water immediately before making a plate cultivation, it is obvious 

 that any conglomerate which may be present and does not yield to this 

 treatment is, for practical purposes, a single source of infection, and 

 will thus give rise to a single colony. 



Another difliculty with plate cultures is due to some species 

 causing liquefaction of the gelatine through the action of peptonising 



* e Komnrissions-bericht iiber die Wasserversorgung von Zurich und ihren 

 Zusammenhang rait der Typhus-epidernie des Jahres 1884,' Zurich, 1885, p. 92. 



t Malapert-Neufville (' Zeitschr. f. analyt. Chem.,' vol. 25, 1886, p. 39), Wollf- 

 hiigel and Biedel ("Die Yermehrung der Bacterien hn Wasser," 'Arb. a. d. K. 

 Gesundheitsarote,' vol. 1, 1886, pp. 455 — 480) ; also Pol and Dunant (' Revue 

 d'Hygiene,' 1885, vol. 7, p. 183). 



X It may be assumed that the shaking carried on for a few minutes only before 

 making a culture can have no effect on the life of the microbes ; even the effect of 

 long-continued shaking is very doubtful, the evidence being quite conflicting. On 

 this point see Horvath ('Pfluger's Archiv f. Physiol.,' vol. 17, 1878, p. 125), 

 Naegeli ('Theorie d. Gahrung,' 1879, p. 88), Reinke (' Pniiger's Arch. f. Physiol.,' 

 vol. 23, 1880, p. 434), Biichner (' Sitzungsber. d. K Bayer. Akad. d. Wiss.,' 1880, 

 pp. 382 and 406), Wernich (' Desinfectionslehre,' 1880, p. 74), and further litera- 

 ture in these. 



§ Elfving used cotton-wool (' Studien u. d. Einwirkung des Lichtes,' p. 31). See 

 also G-eppert ('Ann. de l'lnst. Pasteur,' vol. 3, p. 673), who used glass. 



