70 Microbes and You 



boiling kills all microorganisms. It is not meant to imply that 

 boiling a baby's bottle for ten minutes is not a safe procedure. 

 Quite to the contrary. This common practice is based upon sound 

 scientific principles. Pathogenic bacteria are not normally able 

 to withstand such heat treatment, and the spore-formers which 

 might survive are not likely to cause any upset in the infant who 

 drinks milk stored under proper refrigeration in such a boiled 

 bottle. To a microbiologist sterility means the killing, or the 

 removal, of all living cells, whether they be plant or animal, 

 microbe or whale! 



The living protoplasm of bacterial cells is composed of protein 

 distributed in a well balanced state known as a colloid. Matter 

 is said to be in a coLLomAL state when it is dispersed permanently 

 and so finely that the individual particles cannot be seen with 

 the ordinary microscope, even though the particles may be larger 

 than molecules. Anything that we can do to tip this colloidal 

 protoplasm out of balance is going to adversely affect the organism, 

 and a severe unbalance will result in the eventual death of the cell. 

 We can coagulate cell protein in much the same way that we con- 

 geal an egg by heating it, and such disruption of the colloidal 

 balance is enhanced in the presence of water, as will be evident 

 from the figures in Table 5. 



Table 5 



RELATIONSHIP OF MOISTURE CONTENT TO COAGULATION 

 TEMPERATURE OF EGG ALBUMIN IN THIRTY MINUTES 



Egg albumin +50% water coagulates at 56° C. 

 Egg albumin +25% water coagulates at 74-80° C. 

 Egg albumin + 18% water coagulates at 80-90° C. 

 Egg albumin + 6% water coagulates at 145° C. 

 Egg albumin + NO water coagulates at 160-170° C. 



Boiling. Under certain conditions, in the absence of resistant 

 spores, boiling will free liquids of living cells, but as previously 

 mentioned, since one cannot be sure when spores are present, 

 boiling should not be relied upon to insure bacteriological sterility. 

 An interesting and important sidelight is the influence of elevation 

 upon the boiling point. At sea level water boils in an open con- 



