Physiology of Microbes. 19 



CHAPTER 11. 



PHYSIOLOGY OF MICROBES. 



1. Digestion.— 2. Respiration.— 3. Nutrition.— 4. Movements.— 

 5. Generation and multiplication. — 6. Action of the media 

 upon microbes.— 7. Action of microbes upon the media. — 

 8. Classification. 



I. Digestion. 



1. Foods. — Microbes being destitute of chlorophyll 

 require for their nutrition organic products already 

 formed; consequently they must nourish themselves 

 at the expense of vegetable or animal substances. 

 They borrow nitrogen from albuminoid substances or 

 their derivatives as well as from ammoniacal salts, and 

 occasionally, in part, from nitrates ; carbon and hy- 

 drogen from hydrated carbonaceous substances — 

 sugar, glycerin, and salts of malic, tartaric and acetic 

 acids. 



They require also mineral substances — sulfates and 

 phosphates of sodium, potassium, and magnesium. 



They are very sensitive to the chemical composition 

 of the nutrient medium in which they live ; traces of 

 certain substances,. as well as the absence of others, 

 can bring about profound alterations in the manifesta- 

 tions of their vitality. 



Their medium should be slightly alkaline and very 

 aqueous. Excess of acidity or of alkalinity, acidity 

 especially, is prejudicial to their growth. 



2. Digestion. — The foods of microbes, like those of 



