DISINFECTION 517 
Variability of resistance in the same species. The power of resist- 
ance of the same species of bacterium varies greatly under different 
conditions. For instance, Bear found that a freshly inoculated cul- 
ture of the bacterium of diphtheria was destroyed with 1-5000 of 
nitrate of silver, but that a twenty-four hour culture required 1-1000 
of the same agent to kill it in the same space of time. In some work 
done by Esmarch he made use of anthrax spores from seventeen differ- 
ent sources. They were destroyed by 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. 
The material in which the bacteria exist. The medium in which 
the bacteria exist 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, 
purulent, tuberculous discharges it cannot be trusted to destroy them. 
Again Behring states that sporeless anthrax bacteria in water are 
killed by corrosive sublimate 1—500,000; in bouillon, by 1-40,000; 
but in blood serum not with certainty with a solution of 1-2000. 
Some disinfectants are influenced very much by the character of the 
material which contains the infectious organism, while other disin- 
fectants are influenced to a comparatively slight degree. The 
experimental work which does not take into account the influence of 
the media upon the disinfectant is not of much practical value. 
Temperature. 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 which 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 the temperature under which their 
disinfecting experiments were made. 
Interpretation. In many of the results the inhibitory action of the 
agent in question has been mistaken for its germicidal action. After 
the bacteria have been subjected to the influence of a disinfectant for 
a given time, though not killed, their vegetating and pathogenic 
capabilities may be modified but still able, under favorable conditions, 
to return to their former vigor. 
The rules and recommendations of the various cattle commissions 
and those having authority in methods for the prevention of infectious 
diseases of animals do not very clearly define the procedures best 
