338 STATE BOARD OF AGRICULTURE 



Besides heat, cold may be iucidentally mentioned as a disinfectant. Cold has no 

 power of destroying or devitalizing bacteria. It may stay the growth and develop- 

 ment of bacteria but it falls far short of possessing germicidal or disinfectant prop- 

 erties. 



CHEMICAL SUBSTANCES. 



In chemicals are found agents which may be utilized when heat in any of its 

 forms is not available. The more prominent chemical germicides, disinfectants 

 and antiseptics will be briefly reviewed in order to give the reader a comprehensive 

 knowledge of the substances commonly employed. 



Mercuric Chloride.— This substance is also called corrosive sublimate and bi- 

 chloride of mercury. It is a salt of mercury that has become a very useful and a 

 very common agent with which to fight bacteria. This may be mostly due to its 

 inexpensiveness and the satisfaction which it has given. It may be procured from 

 any druggist at one dollar per i^ound or thereabouts. After the solution has been 

 made and properly diluted there will be a large quantity for disinfectant purposes. 



The great value of mercuric chloride is not recognized by all experimenters, 

 mainly on account of its peculiar action. If, however, its chemical affinities are 

 kept in mind, its action upon bacteria may be easily gained. It has been demon- 

 strated that this salt in solution acts upon the immediate surface of the germs, or 

 perhaps the germ-wall, by forming a coat, which appears to prevent further growth 

 or development of the cell. If this coat be removed, there visually remains sutficient 

 life in the cell to continue its development vmder proper conditions. How long this 

 coat may retard the activity of a cell is still an open question, but it is generally 

 assumed that the cell is eventually killed by the slow penetrating poisonous power 

 of the mercury or is held captive indefinitely by the failure of a solvent to act upon 

 the mercuric cost. 



Yersin has discovered that a solution of one part of mercviric chloride to one 

 thousand parts of water will kill the tubercle bacillus in one minute. On the other 

 hand, Scbill and Fischer with a solution of one part of mercuric chloride to two 

 thousand parts of water were unable to destroy the virulence of tuberculous 

 sputum when equal amounts of the sputum and solution were used. This may be 

 accounted for by the affinity of mercury for the proteid material in the sputum 

 and the consumption of the mercury present by the formation of some insoluble 

 salt which would not allow the mercury to act upon the tubercle bacilli. Accord- 

 ing to Fraenkel, the spores of anthrax are destroyed in thirty minutes by a solution 

 of one to one thousand, but this probably means that the spores are restrained 

 rather than actually destroyed, because the later work with mercuric chloride tends 

 to show ithat the actual destruction of germs or spores does not take place im- 

 mediately or in a very short period. 



Notwithstanding the fact that mercuric chloride may not act as a rapidly de- 

 stroying agent but as a rapidly restraining agent, there is no hesitancy in recom- 

 mending it as a valuable germicide or disinfectant, especially in the absence of 

 albuminous matter. 



The strong affinity which mercuric chloride has for proteid material may be 

 greatly decreased by the use of sodium, potassium or ammonium chloride. With 

 this purpose in view, a concentrated solution of mercuric chloride, together with 

 one of these salts, is prepared as a stock solution and is always ready for use upon 

 dilution. This overcomes a great dlfliculty in the use of mercuric chloride, which 

 is so slow to dissolve in water. The following will give the parts used for a con- 

 centrated solution: 



1 part of mercuric chloride. 



2 parts of sodium chloride (common salt). 

 5 parts hydrochloric acid. 



Five parts of this solution, by measurement, to nine hundred ninety-five parts of 

 water will give a disinfecting solution of one to one thousand. If a solution suffi- 

 ciently dihited for application is desired, the following formula will answer: 



1 part mercuric chloride. 



2 parts sodium chloride (common salt). 

 1,000 parts of water. 



A solution of one to one thousand is perhaps the most commonly used for dis- 

 infecting purposes or as a germicide, but if it is to be used as an antiseptic or as a 

 wash for Avouuds, great care should be exercised to avoid using strong solutions 



