Il6 MANUAL OF BACTERIOLOGY. 



should be superfluous to warn students of the danger to them- 

 selves and others of infecting their hands and surroundings; 

 but some who work in bacteriological laborities become careless, 

 just as do those who work with explosives. The most impor- 

 tant precaution, perhaps, is observance of the rule that while 

 working in the laboratory, nothing should be put in the mouth. 

 Cultures should never be left in improper places. Cultures 

 of bacteria should be thoroughly sterilized before the tubes are 

 cleaned. In some laboratories tubes, dishes and other appara- 

 tus, after use, are placed in the autoclave or in the dry sterilizer 

 or they are soaked in disinfecting solutions; there seems to be 

 no uniform practice in this respect. 



In taking these measures, the same kind of reasoning applies 

 as that which induces engineers to give bridges several times 

 the strength they need to bear the greatest strain likely to be 

 put upon them, or to make the boiler of a steam engine strong 

 enough to bear six times the greatest pressure which it is ex- 

 pected that the steam contained in it will exert. 



