BACTERIA AND THEIR ROLE IN NATURE 1 7 



is protected against invaders. In certain diseased conditions the 

 blood and tissues of man and lower animals become filled with 

 bacteria. Just before and soon after death these bacteria rapidly 

 invade and tear down the body. 



What Are the Functions of Bacteria? — Living in a world 

 teeming with bacteria, we naturally ask this question. They 

 swarm on our bodies and in the alimentary tract. Do they help 

 us or would we be better off without them? 



It is certain that chickens, frogs, and some other animals, if 

 hatched free from bacteria and fed on sterile food, do not grow 

 normally. Bacteria assist cows, sheep, and horses in their diges- 

 tion, but it is doubtful if they are essential in the alimentary tract 

 of man. Inasmuch as we live in a world filled with microbes it 

 is not possible to keep them from the stomach and intestines. 

 Moreover, it is known that some are harmless while others are 

 injurious. Some of the harmless ones produce products which 

 inhibit or prevent the growth of the injurious. Hence, consider- 

 able attention has been given to a study of the conditions favoring 

 the growth of the beneficial microbes in the alimentary tract of 

 man. The good efitects which sometimes follow the use of sour 

 milk and buttermilk are due to their carrying into the intestines 

 beneficial bacteria together with products which favor their 

 growth. Some claim that the rate with which man ages is deter- 

 mined not by the years he has lived but by the microbes which 

 inhabit his digestive tract. 



Bacteria play numerous wonderful parts in the many changes 

 going on in this world. This is true to such an extent that it is 

 hard to conceive of our living in a world without bacteria. Ex- 

 amining the soil from which man draws — either directly or in- 

 directly — his clothing, food, and other necessities of life, we Rnd 

 it to be a veritable garden of minute plants which have been at 

 work within it long before man began to till the soil. What a 

 wonderful change they produce in transforming the bleak, bar- 

 ren rock into a fertile field from which the gardener can gather 

 his delicious berries or beautiful flowers, the farmer his golden 

 sheaves of wheat or his deep green nutritious loads of hay! 



