CHEMICAL AND PHYSICAL PROPERTIES 31 



tents of the cell. The space formerly occupied by 

 the protozoon is vacated and it has moved to a position 

 directed by the pseudopod. In some protozoa a 

 portion of the body has muscular power and drives the 

 body. Again, a portion of the cell wall may be fitted 

 with a sucking apparatus, serving both to drive or to 

 attach the protozoon to another body. They gain 

 their food by simple absorption through the wall or by 

 possessing definite vacuoles or openings for this pur- 

 pose. Excretion takes place the same way. 



Reproduction may occur by simple dividing as in 

 bacteria. Protozoa may divide by simple budding 

 with breaking off of the smaller piece similar in the 

 first stages to the pseudopod. The higher protozoa 

 go through a complicated process of division such as 

 is seen in the higher animal cells, or there may be 

 male and female elements with conjugation. 



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 proteid (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 sub- 

 stances which form the most important foodstuff for 

 animals, the proteids. Chlorides and phosphates of 

 the lighter metals form the inorganic salts. 



The wall of the bacterial cell permits the passage 



