54 LABORATORY EXERCISES IN BACTERIOLOGY. 



deep scrapings from the epiderm, inoculating them as before, in order to 

 determine the degree of penetration of the disinfectant solutions below 

 the surface of the skin. All tubes, properly marked, are now placed into 

 the incubator; and at the usual intervals of one, two, and three days 

 observations made in comparison with the control experiments and the 

 results noted. 



Disinfectant Gases. Disinfection of large spaces, as of sick-rooms, hospital wards, 

 ship-holds, and similar inclosures, is commonly attempted by means of disinfectant 

 gases ; the process being completed by washing the floors, walls, and ceilings as far as 

 practicable, and the furniture, when possible, with disinfectant solutions, as of corrosive 

 sublimate or carbolic acid, all comparatively worthless material burned, and all material 

 which can be safely and conveniently subjected to heat thoroughly baked, boiled, or 

 steamed in the usual manner. The gases commonly used for such purpose are formalde- 

 hyde and sulphurous oxide. When the method is attempted it is essential for success 

 that the exposure shall be a prolonged one, the room being kept filled with the gas for 

 twenty-four hours, and all cracks and crevices about doors and windows carefully closed 

 with strips of paper pasted over them, or by cotton or rag caulking, to prevent the escape 

 of the gas. Of course, all large openings, as of flues, registers, ventilating openings, as 

 well as doors and windows, are to be thoroughly sealed. All clothes, curtains, carpets, 

 and similar substances which it is desired to have disinfected by the gas are to be hung 

 about the apartment in the thinnest possible layers so as to facilitate thorough penetra- 

 tion. When sulphur is to be used, it is best that water should first be evaporated in the 

 room so as to make the atmosphere as moist as possible, such moisture aiding in the 

 penetration of the gas into any fabric exposed ; it is not essential, however, in case for- 

 maldehyde is employed, but is not objectionable. In practice it is customary to burn 

 twenty grams of sulphur for each cubic meter of space, the sulphur being either in the 

 form of the sulphur disinfecting candles or in the powder, when it is well to first moisten 

 it with alcohol. Care should be taken to protect the floor and the room contents from 

 the sulphur flame, either by burning the sulphur in candle form floating upon a wide 

 dish of water (the sulphur upon a board or in a shallow dish), or burning the powdered 

 sulphur in a dish set in a large sand or earth bath. 



In using formaldehyde, from ten to fifteen cubic centimeters of the commercial 

 solution should be evaporated for each cubic meter of space. A number of forms of 

 apparatus have been devised for the purpose of generating this gas ; of these, probably 

 the most efficient are those in which the commercial formaldehyde solution, mixed with 

 glycerine or calcium chloride to prevent its conversion into its solid isomer paraform, is 

 vaporized in a metal retort or tube, by means of an alcohol flame beneath, the gas being 

 discharged from the mouth of the apparatus through a tube, by which it may be con- 

 veyed through a keyhole or other small aperture into the interior of the room to be dis- 

 infected. Or the gas may be obtained by heating the paraform, which may be obtained 

 in pastile form in commerce ; or it may be produced by the action of a heated plate of 

 copper upon the fumes of wood alcohol. Special types of generators based upon each 

 of the latter methods may be had and will serve the required purpose. 



Exercise 20. Three slips of sterile filter paper or thread are soaked 

 in an active culture of one of the pus germs, as of the Micrococcus pyogenes 

 aureus, for an hour. They are then separately inclosed, each in a definite 



