DISINFECTION 



371 



the results of many of the older experiments is that test 

 organisms were used which are very unlike those for which 

 these disinfectants are now wanted. The practical value of 

 the more recent experiments is greater because they have more 

 generally dealt with species of bacteria with which most of the 

 work of disinfection has to do. 



2. The power of resistance of the same species of bac- 

 terium varies greatly under different conditions. For instance, 

 Bear found that a freshh' inoculated culture of the bacterium of 

 diphtheria was destroyed with i :500o of nitrate of silver, but 

 that a twenty-four hour culture required i : 1000 of the same 

 agent to kill it in the same space of time. In some work done 

 by Esraarch he made use of anthrax spores from seventeen 

 different sources. The}' were destroyed b}- steam at 212° F. 

 in from one to twelve minutes and by a five per cent solution 

 of carbolic acid in from two to forty-two days. 



3. The medium in which the bacteria exists influences 

 the results of the disinfectants. The bacterium of tuberculosis 

 from an aqueous suspension dried upon threads may be 

 promptly destroyed by mercuric chloride, but in fresh, puru- 

 lent, tuberculous discharges it cannot be trusted to destroy- 

 them. Again Behring says that sporeless anthrax bacteria in 

 water are killed by corrosive sublimate, i : 500,000 ; in bouillon, 

 by I : 40,000 ; but in blood .serum not with certainty with a 

 solution of I : 2000. Some disinfectants are influenced very 

 much by the character of the material which contains the 

 infectious organism, while other disinfectants are influenced to 

 a comparatively slight degree. The experimental work which 

 does not take the influence of the media upon the disinfectant 

 into account is not of much practical value and failures are to 

 be expected in the work of the disinfector who does not act in 

 accordance with this fact. 



4. The temperature under which the disinfecting agent 

 acts influences very much the rapidity and the certainty of its 

 action. Thus Heider found that anthrax spores that survived 

 the action of a five per cent solution of carbolic acid thirty-six 

 days at ordinary room temperature, were killed in from one to 

 two hours at 131° F. Some investigators have failed to state 



