CRYPTOGAMS 



305 



together under the general head of bacteria. While not re- 

 sponsible for all the disease known to be caused by living 

 organisms, — some very serious ones, such as malaria and 

 cattle fever, being due to animal parasites, — the majority of 

 those that have been most carefully investigated are traced 

 to the bacteria, or other fungi. After any of these parasites 

 have found a lodgment in the body of an organism whose 

 tissues furnish them a congenial habitat, they multiply with 

 enormous rapidity, and through the action of certain poisons 

 called toxins, which they excrete, give rise to the most de- 

 structive diseases in both animals and plants; and no rational 



Figs. 434-437. — Disease-producing bacteria : 434, bacteria of consumption 

 (Bacillus tuberculosis) ; 435, cholera bacillus ; 436, bacilli of anthrax, showing spores ; 

 437, typhoid bacillus. 



sanitary science is possible without a knowledge of their 

 habits and life history. Add to the vast amount of human 

 suffering that is to be laid at their door the economic damage 

 done by rust and smut fungi, by molds and blights and mil- 

 dews, and we shall be tempted to conclude that the " battle 

 of life" is largely a struggle against these invisible foes. 



346. Useful fungi. — Not all fungi, however, are injurious. 

 On the contrary, the great majority of them are harmless, 

 and very many kinds are positively beneficial to man. 

 Without the yeasts and bacteria of fermentation we could 

 not have our bread and cheese. Other forms are active 

 agents in the fertilization of soils, it having been estimated 

 that there are 100,000 or more of these infinitesimal la- 

 borers at work in every cubic centimeter (about ^^ of a 

 cubic inch) of virgin soil ! Even the bacteria of putrefac- 

 tion, which we are accustomed to regard as the embodiment 



