Report on the Bacteriology of Water. 327 



or elastic bands, and the whole then so fixed that the sunlight had to 

 traverse the coloured or other fluid before reaching the agar film in 

 which the spores were embedded. It will, of course, be noticed that 

 the light here traverses three plates of glass as well as the solution 

 of the screen before impinging on the spores in the film, a fact of 

 importance. 



I have summed up the characters and chief properties of the solu- 

 tions employed in the following Table E, and need not, therefore, 

 describe them in detail here. In all cases, excepting N"os. 3 and 5, 

 the medium employed for solution was water ; in these exceptional 

 cases, where carbon bisulphide and alcohol were used, it was neces- 

 sary to have screens devoid of cement. These were met with in the 

 form of certain small glass flasks, shaped like brandy flasks or scent 

 flasks, with a long neck and flat sides ; they are used on the Continent 

 for sealing up cultures of bacteria. 



FIQ. 2. 



nzr 



The chief objection to their use is that the flat sides are apt to be 

 slightly uneven in thickness on the internal face ; by carefully select- 

 ing from a large number, however, I was able to secure several very 

 good screens of this description.* The liquid is, of course, bottled in 

 the usual way, and the neck secured with a good cork. 



VI. 



The following Table F summarises the results of a number of expo- 

 sures behind these screens of coloured and other absorbent media, 

 with particulars as to the dates of exposure, number of hours, insola- 

 tion, and incubation, and other factors worth extracting from the 

 notes. 



It will be observed that I here confined my experiments entirely to 

 the spores of Bacillus anthracis. I did this because it became more 

 and more evident that until I had obtained all the information possi- 

 ble about some one species the factor most constant in this long 

 series of slight variables it would be difficult to value the import- 

 ance of specific differences later. Experience has thoroughly con- 

 firmed the justice of this conclusion. 



* In later experiments I have had the side ground out flat, and glass or quartz 

 plates cemented on. 



