80 



BIOLOGY 



spongy. The bread made from such dough is full of holes, and 

 is more palatable and digestible than bread cooked from dough 

 that has not been rendered light and porous (i.e., unleavened 

 bread). In the case of bread raising and beer making, the yeast 

 as a rule is intentionally planted in the material which is to be 

 fermented. In the making of wines or the making of cider, 

 yeast is not planted. In these cases, the grape juice or the apple 

 juice is allowed to stand undisturbed, and the yeasts that are 

 floating around in the air, known sometimes as "wild yeasts," 

 have an opportunity of getting into the juices, where they grow 

 and produce fermentation. Thus although no yeast has been 

 added to these materials, the fermentation is brought about by 

 yeast exactly as if the yeast had intentionally been added. 



BACTERIA 



The simplest of all known living organisms are the Bacteria. 

 These consist of the extremely minute organisms shown in Figure 



33. Some of them are spher- 

 ical, some are in the form of 

 short rods or long threads, 

 and some spiral. They are so 

 minute that practically no 



FIG. 33. BACTERIA 



A, rod-shaped form, Bacillus or Bacte- 

 rium; 1, Diphtheria bacillus; B, spiral forms, 

 Spirillum; C, spherical forms, Coccus; 2, 

 Streptococcus; D, the method of multiplica- 

 tion by division ; E, the formation of spores, s . 



FlG. 34. A DIAGRAM SHOWING THE 



RELATIVE SIZE OF THE POINT OF 

 A FINE NEEDLE AND BACTERIA 



The small dots at the tip of the needle 

 represent bacteria. 



internal structure can be seen. Some of them are not more 

 tihan 1/50,000 of an inch in diameter; see Fig. 34. Some 



