86 STERILIZATION, DISINFECTION, AND ANTISEPSIS. 



In other substances a 10 percent, dilution would be the last 

 step of the test. Thus are obtained results which are fixed 

 and definite, stating positively the strength of disinfection 

 used and the time of its application. 



Cautions. In conducting these experiments one must 

 remember always that the growth of bacteria on the solid 

 tubes may be considerably retarded by the action of the dis- 

 infectants, and one must not accept the result as conclusive 

 unless those cultures have been kept under observation for a 

 considerable length of time. Again it is proper, whenever 

 practicable, to conduct the experiments at the temperature of the 

 human body, 37 C., as experience has demonstrated that at 

 this and higher temperature the disinfectant power of chemicals 

 is increased. 



THE METHODS OF ANTISEPSIS. 



Substances that retard the growth of bacteria without, 

 however, destroying them are called antiseptics. It is clear 

 that all disinfectants when used in a more diluted form, or 

 when allowed to act for a shorter space of time than is re- 

 quired for them to show their germicidal power, act as anti- 

 septics. 



I. The Common Disinfectants. 



Carbolic acid, strength 3 to 5 per cent., efficient in one hour. 



Bichloride of mercury, solution 1 : 1000 or 1 : 500, acts from 

 within a few minutes to a half-hour. 



Chlorinated lime, containing free chlorine, is an efficient 

 germicide in an hour's time in the strength of from 5 to 

 10 per cent. 



Boiling water, to which 2 or 3 per cent, sodium carbonate 

 is added, is an efficient germicide in an hour. 



Sulphur dioxide gas, when used dry, has little or no disin- 

 fectant power, and bacteria have been able to withstand an 

 atmosphere containing from 10 to 12 per cent, of this gas for 

 several hours. In the presence of moisture, however, it 



