Excretions 



18 



HOUSEHOLD BACTERIOLOGY. 



is endowed with all the characteristics of living matter 

 anywhere. 



All living things whether plant or animal take 

 food in some way. All, too, having taken food, 

 change it over into their own substance and give out 



FIG. 9. DIFFERENT FORMS OF SPIRILLA. 



some 'of the results of these changes as waste prod- 

 ucts in the form of gases, liquids, or solids. 



Bacteria are no exception to this universal rule. 

 Their products are either gases or liquids and these, 

 dissolved in blood or other liquids, bring about vari- 

 ous changes, the results of which may be either de- 

 sirable or undesirable, according to the nature of the 

 bacterium, the amount of the excretion, or other con- 

 ditions under which the changes are wrought. 



The processes of bacterial growth in the human 

 body and in food substances are similar. 



