CHAPTER XL 

 DISEASES CAUSED BY PROTOZOA. 



IN the classification of micro-organisms in chaj>- 

 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 o>f 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 pro- 

 tozoa is peculiar in that part is lived inside 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 is found quite fre- 

 quently in the Southern States and occasionally in the 

 Northern States. It is caused by the Ameba histo- 



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