184 



CRYPTOGAMS 



A common sjDherical form is ^ q q^q q q inch in 



Bacteria 



441. Tlie Bacteria (Fig. 301) include the smallest of 

 all living organisms. Even the highest powers of the 

 microscope fail to show much of their inner structure ; 

 so that at present very little is known of their relation- 

 ship to other groups. Our knowledge is confined to their 

 external forms, methods of multiplication, and modes of 

 life, with their effects, good and bad ; but this knowledge 

 is of the highest practical importance, since the Bacteria 

 affect the lives of other living beings, including man, in 

 very direct ways. 



442. Size. 



diameter ; the rod-shaped germ of consumption is from 

 three to nine times as long as this ; many species, however, 



are considerably larger. Form. The 

 principal forms are (1) spherical, 

 (2) straight cylindrical, (3) spiral. 

 Movements. Many Bacteria exhibit 

 very lively movements. Locomotion 

 is usually accomplished by means of 

 extremely fine cilia (Fig. 301). Mul- 

 tiplicatio7i commonl}^ takes place by 

 fission. Each individual divides into 

 two parts, by transverse division, 

 each part becoming a new individual. 

 Under favorable conditions — abun- 

 dance of food and considerable 

 warmth — the Bacteria ma}" double 

 in numbers about every half hour. 

 In this way enormous multitudes may 

 result even from one original indi- 

 vidual in a comparatively short time. 

 Low temperatures retard growth and 

 division : hence the utility of ice in preserving foods in 

 warm weather. Under certain conditions Bacteria pass 

 into a spore condition, in which they become higlily 

 resistant to destruction by heat or drying. In a dry 



301. Bacteria, highly mag- 

 nified : a, the germ 

 of typhoid fever, 

 stained to show the 

 cilia; h, a spiral 

 ciliated form ; c, a 

 rod-shaped form, in 

 chains ; d, a spheri- 

 cal form. — a, b, 

 from ExGLER and 

 Prantl. 



