CHEMICAL AND PHYSICAL PROPERTIES 33 



CHEMICAL AND PHYSICAL PROPERTIES. 



Bacteria. Chemically the bacterial body is composed 

 chiefly of water (80 to 90 per cent.), the remaining 

 part being made up of protein (see below), fatty 

 matters, including waxes, a trace of the carbohydrates 

 (sugars and starches), and inorganic material. The 

 cellulose supposed to be characteristic of vegetable 

 cells is present in very small quantities. The largest 

 part of the solid matter is comparable to the organic 

 substances which form the most important foodstuff 

 for animals, the proteins. Chlorides and phosphates 

 of the lighter metals form the inorganic salts. 



The wall of the bacterial cell permits the passage 

 of fluids containing foodstuffs, and is therefore com- 

 parable to the wall of other vegetable and animal 

 cells. 



Protozoa. The chemical composition is probably 

 like that of bacteria, although little is known of it. 

 Their vital activities are influenced by physical con- 

 ditions, as is the case with all animate beings. They 

 require moisture for their full development, but may 

 live for indefinite times when it is at a minimum. A 

 definite temperature is demanded by each species or 

 genus for its full activity. They are susceptible to 

 high degrees and remain quiescent in nature in the cold 

 for a long time. Desiccation of the germinating forms 

 is usually fatal, but when in sporulation or encystment 

 drying is more easily withstood. Light is not abso- 

 lutely essential for the growth of protozoa, but they 

 are usually attracted or repelled by it; that is, few 

 if any are indifferent to luminosity. 



