8o METHODS OF CULTIVATION OF BACTERIA. 



amount of water vapour in the interior by having in the 

 bottom of the incubator a flat dish full of water from which 

 evaporation may take place. Tubes which will require to 

 be long in the incubator should have their plugs covered 

 either by india-rubber caps or by pieces of sheet rubber tied 

 over them. These caps should be previously sterilised in 

 i-iooo corrosive sublimate and then dried. Before they are 

 placed on the tubes the cotton-wool plug ought to be well 

 singed in a flame. " Cool " incubators are often used for 

 incubating gelatine at 21 to 22 C. Here again Hearson's 

 design is as good as any in the market. 



General Laboratory Rules. On the working bench of 

 every bacteriologist there should be a large dish of i-iooo 

 solution of mercuric chloride in water. Into this all tubes, 

 vessels, plates, hanging-drop cultures, etc., which have con- 

 tained bacteria and with which he has finished, ought to be 

 at once plunged (in the case of tubes the tube and plug 

 should be put in separately). On no account whatever are 

 such infected articles to be left lying about the laboratory. 

 The basin is to be repeatedly cleaned out. All the glass 

 is carefully washed in repeated changes of tap water to 

 remove the last trace of perchloride of mercury, a very 

 minute quantity of which is sufficient to inhibit growth. 

 Old cultures which have been stored for a time and from 

 which fresh sub-cultures have been made ought to be 

 steamed in the Koch's steriliser for two to three hours 

 or in the autoclave for a shorter period and the tubes 

 thoroughly washed out. Besides a basin of mercuric 

 chloride solution for infected apparatus, etc., there ought 

 to be a second reserved for the bacteriologist's hands in 

 case of any accidental contamination of the latter. In 

 making examinations of organs containing virulent bacteria, 

 the hands should be previously dipped in i-iooo mercuric 

 chloride and allowed to remain wet with this solution. No 

 food ought to be partaken of in the laboratory, and pipes, 

 etc., are not to be laid with their mouth-pieces on the 

 bench. No label is to be licked with the tongue. Before 

 leaving the laboratory the bacteriologist ought to wash the 



