398 MICROORGANISMS 



latter half of the nineteenth century that the science of bacteri-* 

 ology had its wonderful development. This development of a 

 science from the faintest beginnings to one that ranks in the 

 very forefront of the various branches of knowledge within the 

 time of a single generation, is very largely the work of two 

 great men. These men are Louis PASTEUR (Fig. 269) who 

 may be called the father of bacteriology and ROBERT KOCH 

 (Fig. 270) who may be said to be the man who made bacteri- 

 ology an independent science. You should improve the first 

 opportunity to learn something of the personal lives and of 

 the work of these men. 



Exercise 92. Study of a Hay Culture 



Fill a large glass jar with water, preferably water from some 

 pond or stagnant pool, and put a good sized handful of timothy 

 hay into the water. The hay should be cut into small pieces before 

 it is put into the water. Place the jar in a warm place and continue 

 to study the organisms that appear in it for several days. If the 

 temperature of the water does not fall below 70F. you should find 

 it teeming with bacteria at the end of 24 or 48 hours. Bacteria 

 will continue to be abundant in the culture for several weeks. If 

 you study a sample of the water about every other day for a period 

 of two or three weeks, you will find that different forms of bacteria 

 will be most abundant at different times. If the jar is allowed to 

 stand for a month or two, all bacterial action will finally cease and 

 the water will become quite clear. Can you suggest the reason 

 for this? 



452. Life History of a Hay Culture. Along with the dif- 

 ferent kinds of bacteria which from time to time will appear 

 in the culture, you will find a great many different kinds of 

 microscopic animals. As you study the culture from time to 

 time, you will find that each kind of animal, like each kind 

 of bacterium, will seem to have its day and then gradually 

 disappear to give place to some other form. The reason for 

 this shifting panorama of life which a culture like this exhibits 

 is found in the varying chemical conditions of the culture which 

 are brought about by the organisms themselves. Thus, a 

 given organism becomes the leading type whenever the con- 



