338 FOUNDATIONS OF BOTANY 
Perhaps the most interesting, certainly to us the most 
practically important, cases of parasitism are those in 
which the bodies of animals, and especially of men, are 
attacked by parasitic plants. Bacilli and other bacteria 
of many species (Sect. 263) are among the commonest 
parasites which use the bodies of animals as hosts, and 
two or three examples will serve to illustrate how they 
find a lodgment in the host. 
Rich garden soil, the dust of stables, and a good many 
other sources often contain immense numbers of a bacil- 
lus! which causes lockjaw. A man in cleaning harness 
scratehes his hand with a buckle, introduces the bacilli 
into his system, and is soon taken with an attack of lock- 
jaw. Sewage water often swarms with the bacilli of 
typhoid fever? (Fig. 174). The people in a city drink 
unfiltered water from a river into which sewage has been 
allowed to run higher up stream,-the bacilli multiply at a 
rapid rate in the intestines of those who have drunk the 
water, and many of them are taken sick with typhoid 
fever. The phlegm expectorated by consumptive patients 
is full of the consumption bacillus ;? this phlegm becomes 
dried up on floors, streets, or sidewalks, it is breathed by 
every one in the form of fine dust, and in the lungs of 
many who breathe it colonies of the bacillus are formed 
and the disease (consumption) becomes established in 
these persons. 
' 408. Enslaved Plants. —Cases in which one kind of 
plant is useful in procuring food (or the raw materials 
of food) for another kind are quite common. 
The relations on which alge and fungi live together in 
1 Bacillus tetani. 2 Bacillus typhi. 3 Bacillus tuberculosis. 
