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 
434 435 436 437 
Fics. 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 
