482 



BACTERIOLOGICAL ANALYSES 



The following table shows the effect of different per- 

 centages of carbolic acid upon B. coli for varying con- 

 tact times, compiled from an experiment conducted 

 under the standard conditions referred to under Envi- 

 ronment. The results closely correspond to those 

 recorded by the Lancet Commission on Disinfectants, 

 1909. 



=No growth, i.e., bacteria killed. 

 + = Growth, i.e., bacteria still living. 



From this it will be seen that the following per- 

 centage solutions will need to be prepared, namely: 

 i.i per cent., i.o per cent., 0.9 per cent., 0.75 per cent., 

 0.7 per cent., as controls for each experiment. 



Prepare solutions of varying percentages by weighing 

 out the quantity of carbolic acid required for each and 

 dissolving in 100 c.c. of pure distilled water in an ac- 

 curately standardised measuring flask. The solutions 

 must be prepared freshly as required each day. 



Environment. 



a. General. 



Close the windows and doors of the laboratory in 

 which the investigation is carried out, to avoid 

 draughts. Flush over the work bench and adjacent 

 floor with i : 1000 solution of corrosive sublimate. 



