22 THE STORY OF GERM LIFE. 



that these 281,500,000,000 would form about a 

 solid pint of bacteria and weigh about a pound. 

 At the end of the third day the total descendants 

 would amount to 47,000,000,000,000, and would 

 weigh about 16,000,000 pounds. Of course these 

 numbers have no significance, for they are never 

 actual or even possible numbers. Long before 

 the offspring reach even into the millions their 

 rate of multiplication is checked either by lack of 

 food or by the accumulation of their own ex- 

 creted products, which are injurious to them. But 

 the figures do have interest since they show faint- 

 ly what an unlimited power of multiplication these 

 organisms have, and thus show us that in dealing 

 with bacteria we are dealing with forces of al- 

 most infinite extent. 



This wonderful power of growth is chiefly due 

 to the fact that bacteria feed upon food which is 

 highly organized and already in condition for ab- 

 sorption. Most plants must manufacture their 

 own foods out of simpler substances, like carbonic 

 dioxide (CO 2 ) and water, but bacteria, as a rule, 

 feed upon complex organic material already pre- 

 pared by the previous life of plants or animals. 

 For this reason they can grow faster than other 

 plants. Not being obliged to make their own 

 foods like most plants, nor to search for it like 

 animals, but living in its midst, their rapidity of 

 growth and multiplication is limited only by their 

 power to seize and assimilate this food. As they 

 grow in such masses of food, they cause certain 

 chemical changes to take place in it, changes 

 doubtless directly connected with their use of the 

 material as food. Recognising that they do 

 cause chemical changes in food material, and re- 

 membering this marvellous power of growth, we 



