SUMMARY 115 



It is fermentation of substances containing nitrogen 

 putrid fermentation. 



The products of these fermentative changes are 

 gases which give odors ; acids lactic, acetic and bu- 

 tyric ; weak alcohol, occasionally, and ptomaines 

 which, when poisonous, are called toxines. 



When putrefaction has ended and the disagreeable Deoay 

 products have disappeared, the residue is usually harm- 

 less and inoffensive. If the processes of decomposition 

 go on in an abundance of oxygen, decay is usually 

 reached without offensive products. 



Sterilization is the removal of all life and is effected 

 by steam, dry heat, chemicals, or filtration. 



To remove bacteria, air may be filtered through cot- 

 ton wool and liquids through unglazed clay or similar 

 substances. 



An antiseptic retards or prevents growth. A dis- 

 infectant kills. 



Some substances are antiseptic or disinfectant ac- 

 cording to their strength or the conditions under 

 which they act. Sunshine is Nature's free disin- 

 fectant; light is commonly an antiseptic, and may be 

 a disinfectant. Dryness, excess of moisture, salt, 

 strong acids, the essential oils, soap, hot water, etc., 

 may be antiseptic with some species and disinfectants 

 with others. 



Pasteurisation, chiefly applied to milk and cream, 

 is a process for killing certain germs which cannot 

 endure the temperature of 155 to 165 F. for twenty 



