1898.] MICROSCOPICAL JOURNAL. 137 



The lecturer then described the methods now in use of 

 cultivating bacteria in solid media, and whicli were first 

 introduced in 1881-82 by Robert Koch. It was men- 

 tioned in passing how great were the benefits conferr^Ml 

 upon humanity by the rapid increase in our knowledge 

 of bacteria, due mainly to these methods, especially in 

 the departments of medicine, chemistry, and botany. 

 A series of slides was then shown, illustrating the culti- 

 vation of bacteria by the use of solid media, their 

 identification by appropriate methods of culture and 

 various modern methods of artificial staining. It was 

 shown how bacteria may thus be sifted out and deter- 

 mined specifically by accurately noting their morpho- 

 logical and biological characters. One slide showed a 

 culture of some bacteria collected in Oxford Street at 

 mid-day, by exposing a bottle containing beef-broth to 

 the air for a few minutes. A portion of the broth was 

 mixed with gelatin, spread on a glass plate 3g inches 

 (88 '9 mm.) in diameter, and placed for a few hours in an 

 incubator. The result of this treatment was that the 

 isolated bacteria multiplied enormously and founded 

 colonies, which could be transferred to other portions of 

 the nutritive medium and sub-cultures so obtained. 

 A sample of sewage was diluted to a known extent, 

 mixed with a definite quantity of medium, and similarly 

 treated. In this way it is possible not only to identify 

 and sift the multitudinous forms of bacteria, but also to 

 estimate their nnmber and roughly compute their 

 weight. Thus the sewage was found to contain about 

 2,000,000 typhoid bacteria per cubic centimetre, and it is 

 estimated that about 40,000 million Staphylococcus aureus 

 weigh 1 gramme. 



The lecturer showed conclusively the absolute futility 

 of chemical analysis, of water, unless it is supplemented 

 by a careful bacteriological examination. It has Ixmmi 

 stated by the most eminent authorities on water analysis 



