Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER III STERILIZATION OF GLASSWARE. PREPARATION OF CULTURE MEDIA In order to become familiar with the characteristics of any given species of bacteria, it is necessary, first of all, to isolate it from every other form. In nature it is seldom that one species is found growing alone. This does occur in certain diseases, but generally speaking bacteria have to be taken from their natural surroundings and grown on artificial food medium in order to be studied. The first essential then for bacterial study is to provide conditions whereby one species may grow, without an admixture of other forms. Since bacteria are practically everywhere this can only be accomplished by first destroying all germs in the food medium on which the organism is to be cultivated and on all apparatus likely to come in contact with it. In order to do this one form or another of sterilization is employed, the method used depending largely upon the object to be sterilized; the underlying principle of each, however, is the destruction of bacteria by heat. Hot air or " dry heat " is generally used for glassware and hot water or steam, " moist heat," for culture media. Cleaning of Glassware. — Before sterilization each article of glassware should be perfectly clean. New glass as a rule only requires washing with soap and water and the adherent dirt removed with a test-tube brush. Old glassware containing cultures should be sterilized either in the autoclave or boiled in 5 per cent solution of washing soda or soapsuds for one hour in a covered boiler. Glassware may be further cleansed if necessary by placing for one hour or more in the following chromic acid mixture: Bichromate of potassium 6 parts Water 100 parts Sulphuric acid 6 parts Dissolve the bichromate by heating in an agate kettl...