60 



LABORATORY EXERCISES IN BACTERIOLOGY. 



and perhaps are contaminated by infectious material, the process of cleansing requires 

 more care and detail. It is not free from possible danger, and the student should exer- 

 cise all the caution and fulfil all the steps indicated in the folio wing directions for its per- 

 formance. The contaminated tubes having been collected, the operator should remove 

 the old cotton stoppers, grasping them with a strong pair of dissecting forceps (subse- 

 quently to be sterilized by flaming), and deposit them at 

 once in one of the laboratory waste jars containing a large 

 amount of one of the disinfectant solutions. This material 

 should be burned subsequently. Each tube, after the re- 

 moval of the stopper, is to be filled even with its lip with 

 a strong disinfectant solution (as water containing five per 

 cent, each of carbolic and hydrochloric acids), and allowed 

 to stand for from twelve to twenty-four hours, in which in- 

 terval it is probable the destruction of any living infection 

 will have been accomplished. The contents of the tubes 

 are now poured with as little spattering as possible into 

 one of the waste jars and subsequently burned. As emp- 

 tied, the tubes are placed in a suitable vessel containing 

 water to which has been added sufficient washing soda to 

 render it distinctly alkaline (two or three per cent.) , in which 



they are to be boiled for an hour. This done, there is no longer danger of infection, and 

 each tube is now thoroughly washed and brushed in clean hot water, the outside surface 

 being wiped clean with a wash-cloth. The tubes are next placed for a few minutes in 

 a weak solution of one of the mineral acids, as in case of new tubes, to neutralize any 

 remaining alkali, rinsed in clean water and placed in inverted position on the draining 

 board to dry. 



FIG. 12. WIRE BASKET 

 FOR TEST-TUBES. 



'*0 r 



FIG. 13. Roux's POTATO 

 TUBE. 



FIG. 14. FERMENTATION 

 TUBE. 



vmf 



YIG. 15. FERMENTATION 

 TUBE. 



Cotton Plugs. The next step of the preparation is the application, in the open end 

 of each tube, of a cotton stopper to prevent the entrance of contaminating organisms 

 from without (v. Ex. 13). These stoppers should be of such a size that when fitted into 

 the mouth of the tube the latter may be sustained easily when lifted by the hand grasp- 



