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 

 scratches 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 2 (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 di'unk 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 algse and fungi live together in 



1 Bacillus tetani. ^ Bacillus typhi. ' Bacillus tuberculosis. 



