544 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



vent its progress b}' the use of disinfectants. Tliere is no royal 

 road to safety in such a case, for the medium of contagion is the 

 atmospheric air, the common reservoir from which all classes, the 

 good and bad, the wise and ignorant, the rich and poor, alike 

 draw at every breath their quota of oxygen, it seems a self-evident 

 proposition that the whole community are or may be, sooner or 

 later, equally interested in the efficaciou&ness of disinfectants. 



The ancients erroneously supposed there Avere but four elemen- 

 tary substances, earth, water, air and fire. We may, however, take 

 these simple divisions as types of the different processes of disin- 

 fection. 



First. Earth acts as an a1)sorbcnt of liquids and gases. At the 

 head of the solid absorbants stands charcoal, which not only col- 

 lects and retains noxious gases, but brings them into such close 

 contact that their decomposition is hastened. Fresh burnt lime, 

 when slacked by water, Avill combine with not less than eighty 

 times its bulk of carbonic acid gas, giving off at the same time the 

 water absorbed in slacking, thus overcharging the air with moisture. 



Second. Water, as the great solvent, which, in the process of 

 washing, carries off in solution many noxious compounds. 



Tldrd. Air, as the great purifier by substitution. Fresh air, dis. 

 placing foul air in the process of ventilation, constantly bears 

 away deleterious exhalations, until the cause of action has been 

 exhausted. 



Fourth. Fire, the result of oxidation, may be taken as the tj'pe 

 of purification by rapid chemical changes. Under this head the 

 most efficient disinfectants should be enumerated. Air is cleansed 

 by abstracting its impurities, or changing their character by disin- 

 fectants, which either decompose noxious bodies, or combine with 

 such bodies so as to form new and harmless substances. 



The most powerful disinfectants are gaseous. By the law of 

 diffusion, they are borne very rapidly and equally into every part 

 of the foul air, and reach the innermost recesses of its hiding 

 places. Furthermore, they are strongly electro-negative when 

 consisting of a single element. 



The chairman concluded by reference to an interesting extract 

 from a foreign paper, which was then read by Dr. J. B. Rich. 



Dr. L. Bradley said that anything that tends 1o dessicate or dry 

 the air, or to enlarge its capability of absorbing and dissolving the 

 fluids of perspiration, is a true disinfectant. Fire increases the 

 power of evaporation. Chloride of calcium and other delc(piescent 



