CHAPTER XI. 
DISEASES CAUSED BY PROTOZOA. 
In the classification of micro-organisms in Chap¬ 
ter II, they were divided into two great classes: those 
belonging to the animal and those belonging to the 
vegetable kingdom. So far we have studied only the 
vegetable micro-organisms—the molds, yeasts, and 
bacteria. The protozoa (sing, protozoon) represent 
the lowest form of animal life, and are composed of a 
single cell made up of a nucleus surrounded by a mass 
of protoplasm. The protoplasm is concerned with the 
nutrition of the cell, while the nucleus controls the 
vital functions, particularly reproduction. Compara¬ 
tively few of the many species of protozoa are known 
to be pathogenic for man. The life cycle of the proto¬ 
zoa is peculiar in that part may be lived in the body of 
some animal, and part outside the body. During the 
cycle they may take on various shapes and sizes. 
Amebic Dysentery. 
This is a chronic form of dysentery, frequently 
associated with abscess of the liver, which is especially 
prevalent in the tropics, in fact the disease is some¬ 
times called tropical dysentery. It occurs frequently 
in the southern part of the United States. Two cases, 
one with abscess of the liver, have come under the ob¬ 
servation of the writer. In both instances the patient 
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