44 LABORATORY EXERCISES IN BACTERIOLOGY. 



strength. In use this solution, as all others of the chemical disinfectant solutions, 

 should be allowed, for action, from half an hour to any longer period which can profita- 

 bly be permitted, and should always be used in great excess of volume. All waste and 

 useless materials thus sterilized should be subsequently burned to obviate the danger of 

 failure of sterilization ; and any articles to be further used should be well rinsed in sterile 

 water before being employed. 



Among the other salts of mercury the iodide and the nitrate, in practically the same 

 proportions as the chloride, may also be employed in disinfection. 



Carbolic acid is probably superior to any of the metallic salts in the certainty of its 

 disinfectant action, but is slower and should be kept in contact with the objects to be 

 sterilized for periods ranging from an hour to twenty-four hours in length. It is usually 

 used in solutions of two and a half to five per cent, strength. The addition of an equal 

 proportion of hydrochloric acid to the solution materially increases its activity, and 

 forms one of the most valuable laboratory disinfectants. It also forms an inert com- 

 pound with organic substances with which it comes in contact, but to a considerably less 

 degree than the metallic salts, to which it is therefore superior. 



Formaldehyde possesses valuable germicidal action if used in solutions of from ten 

 parts of the commercial article (a forty per cent, watery solution of formaldehyde gas) 

 to 1000 parts of water, to forty parts to 1000 of water. It has little penetrative power 

 into albuminous substances, however, and must be granted considerable time for its com- 

 plete action. Its odor and irritant properties prevent its general use. 



Chlorinated lime is one of the most valuable disinfectants, in fresh solution, which 

 we possess, depending upon the free chlorine evolved by its decomposition. It should 

 be used in solutions of from one to three or four per cent, strength, made from the fresh 

 commercial substance as required for use, as it readily decomposes. Articles to be ster- 

 ilized should be kept in contact with an excess of such solution for at least an hour; and, 

 as is always required, should be subsequently rinsed in sterile water if intended for 

 further use. It is an excellent disinfectant in the sick-room for sterilization of clothing 

 or dejecta, and may be profitably used in the laboratory waste jars for preliminary disin- 

 fection of the matter therein collected for combustion. Ordinary lime in strong (twenty 

 per cent.) solution (milk of lime or whitewash) is an excellent crude disinfectant, espe- 

 cially useful in the purification of dejecta from subjects of such infections as typhoid 

 fever or cholera. 



Copperas (ferrous sulphate), commonly used as a disinfectant in urinals and cess- 

 pools, is of comparatively feeble germicidal value, but possesses considerable power as a 

 deodorant. Potassium permanganate, frequently employed in one of the steps of sur- 

 gical disinfection, is of little value, even in comparatively strong solution. 



For discussion of the numerous other agents employed in disinfectant solution, 

 reference should be made to the various text-books upon bacteriology. 



Antiseptic Solutions. Of the antiseptics, borax, boracic acid, iodoform (from the 

 iodine set free from its gradual decomposition), many of the essential oils (as of cinna- 

 mon, cloves, thyme, mint, and other plants) , as well as weak solutions of the disinfectants, 

 may be mentioned. Oil of mustard is both antiseptic and deodorant, but is too irritant 

 for common use ; the dry mustard meal is often used to remove odors from the hands 

 after performance of post-mortem operations and similar work. The retardation of de- 

 velopment of any germ by such substances is not the only phenomenon of antisepsis. 

 In addition to or in place of prevention of growth, the presence of such substances may 

 modify the mode of multiplication (perhaps inducing sporulation), the physical charac- 

 ters of the resultant colonies (as in shape or color), or the pathogenic virulence or other 



