184 Profs. P. F. Frankland and Marshall Ward. 



disease in particular, which has taken place within the past fifteen 

 years, has been watched by those who have had to devote much 

 attention to the sanitary aspects of water-supply. 



The subject of our particular enquiry is, therefore, a modern one, 

 and may be regarded as having been made amenable to successful 

 treatment by the introduction of Koch's method of gelatin e-plate 

 cultures in 1881, and subsequent improvements on the same* 



The publication by Koch of his beautiful and comparatively simple 

 methods of bacteriological study gave an impulse to this kind of work 

 throughout the civilised world. These methods, in spite of certain 

 imperfections from which they never professed to be free, at once 

 opened up the possibility of solving a number of problems con- 

 nected with water-supply which had long been matters of dispute 

 and speculation amongst hygienic authorities. 



As is now well known, Koch's method of gelatine-plate culture 

 admits of an estimate being made of the number of living germs 

 present in a given quantity of any material. That this estimate is a 

 very rough one, and that there are a number of different kinds of germs 

 which it is incapable of revealing, was also known, and has been more 

 or less admitted from the outset. Now this possibility of estimating 

 the number of microbes in a given volume of water has been largely 

 made use of by numerous investigators for a number of different 

 purposes. 



In the first instance, this method has been extensively employed 

 both in this country and abroad for determining the relative richness 

 in micro-organisms (capable of developing in gelatine) of various 

 natural waters. On the Continent, and more especially in Germany, 

 it was assumed that the relative numbers of microbes present in 

 different waters afforded evidence of the extent to which they had 

 been contaminated, and there were not wanting those who hastily set 

 up arbitrary standards of purity based upon a most limited experience 

 of the number of micro-organisms revealed by the gelatine test. By 

 those who were simultaneously employing the method in this country 



* Koch's first announcement of his new method was made at the meeting of the 

 International Medical Congress in London, in August, 1881 (see ' Quart. J ourn. 

 Microsc. Sc.,' Oct., 1881, p. 650), and then published in the ' Mitth. aus d. K. Gresund- 

 heitsamte,' vol. 1, 1881 (see also ' Berl. Klin. Wochenschr.,' 1882, No. 5) . It should be 

 noted, however, that Koch's gelatine-plate method was an improved adaptation of one 

 introduced long before by the botanists Brefeld and Klebs (see Brefeld, "Methoden 

 zur [Inters, der Pilze," 'Abh. der Phys.-Med. G-esellsch. in Wurzbiirg,' 1874 ; also 

 4 Landwirthsch. Jahrb.,' vol. 4, H. 1, and ' Unters. tiber Schimmelpilze,' 1881, H. 4 ; 

 also Klebs, " Beitr. zur Kenntn. d. Mikrokokken," ' Arch, fur exp. Pathol.,' vol. 1, 

 1873, and De Bary, ' Lectures on Bacteria,' Engl, ed., 1887, p. 35). A fair view of 

 the matter is given by Hueppe, ' Die Methoden der Bakterien-Forschung,' 1885, 

 p. 103. To Koch belongs the credit of having applied these plates to the purpose 

 of separating the various colonies of mixtures of micro-organisms. 



