34 AMCEBA, VORTICELLA, PARAMECIUM 



all of these simple animals have sensation, because they 

 respond to irritation. 



Another thing is important to note in our study of the 

 foregoing animals. Beginning with the amoeba, we went 

 steadily upward to higher and more complex forms. The 

 amoeba had no wall, all the others had. The amceba had 

 no mouth, all the others had. The amoelja moved slowly 

 and in a very primiti^•e way, the paramecium faster, while 

 the vorticella had the most complex movement of all. 

 Moreover, it will he recalled that the amoeba moved in any 

 direction, and that almost any part of the body seemed 

 capable of liringing about this movement. The amceba 

 has no sliarply defined anterior and posterior ends, and no 

 right and left sides. The paramecium has a posterior and 

 anterior end and moA'es principally in one direction with a 

 definite jjart of its structure foremost. 



Economic importance of the Protozoa. — Although the 

 protozoans are microscopic in size, some of them exercise 

 a very profound influence upon the life relations of man. 

 Occasionally certain species become so numerous in drink- 

 ing water that the water is rendered unfit for use. A species 

 of amceJDa is known to sometimes occur in the intestinal tract 

 of man and has been thought, Ijy some, to be the cause of 

 dysentery. 



Texas fever, so universally pi-esent among the cattle of 

 the Southern states, is caused by one of these microscopic 

 animals. This oi-ganism is injected into the blood of an 

 animal and carried from one animal to another by the 

 common cattle tick. Whi^nevei- cattle south of what is 

 known as the lick line come in contact with cattle north of 

 that line, tlie latter are inoculated by the tick and usually 

 die. 



