310 METHODS OF IDENTIFICATION AND STUDY 



Chrysoidin (for red) . 

 Malachite green (for green) . 

 Eosin, bluish (for blue) . 

 Methyl violet (for violet) . 



4. Expose the plates, thus prepared, to bright day- 

 light (but not direct sunlight) for varying periods, and 

 complete the observations as in the preceding experi- 

 ments. The bactericidal action of light appears to 

 depend upon the more refrangible rays of the violet 

 end of the spectrum and is noted whether the red yellow 

 rays are transmitted or not. 



5. Control the results. 



NOTE. The ultra-violet rays obtained from a quartz mercury 

 vapour lamp destroy bacterial life with great rapidity under labo- 

 ratory conditions. 



(C) Heat. (Vide Thermal Death-point, page 298.) 



(D) Antiseptics and Disinfectants. The resistance 

 exhibited by any given bacterium toward any specified 

 disinfectant or germicide should be investigated with 

 reference to the following points: 



(A) Inhibition coefficient i. e., that percentage of 

 the disinfectant present in the nutrient medium which 

 is sufficient to prevent the growth and multiplication 

 of the bacterium. 



(B) Inferior lethal coefficient i. e., the time expo- 

 sure necessary to kill vegetative forms of the bacterium 

 suspended in water at 20 to 25 C., in which the disin- 

 fectant is present in medium concentration (concen- 

 tration insufficient to cause plasmolysis) . And if the 

 bacterium is one which forms spores, 



(C) Superior lethal coefficient i. e., the time expo- 

 sure necessary to kill the spores of the bacterium under 

 conditions similar to those obtaining in B. 



The example here detailed only specifically refers 

 to certain of the disinfectants : 



viz:- Bichloride of mercury; 



