476 PROTOZOA 



chromatin. The micronucleus also varies in size and shape but is vesic- 

 ular in structure, with the chromatin heaped in one mass. Division 

 of the nuclei takes place by mitosis in the case of the micronuclei, and 

 by amitosis, as a rule, in the case of the macronuclei. Under unfavor- 

 able conditions the ciliata may encyst. 



Conjugation is necessary to the life activity of these organisms. The 

 phenomena of conjugation in the ciliata has been well worked out. The 

 micronuclei play the most important part, whereas the macronuclei 

 simply break up and disappear in the protoplasm. 



According to the arrangement of the cilia the ciliata are divided into 

 the five orders given in the general classification. Among these the 

 second, the order of the Heterotricha, interests us. In the Hetero- 

 tricha the cilia are uniform over most of the body, while a special- 

 ized set fused into a series of firm vibratory plates are found about 

 the mouth. 



Only one genus the Balantidium, described in a later chapter 

 has been observed in man. 



A description is also given of various protozoan-like forms found in 

 the following diseases : smallpox, cowpox, and related diseases ; scarlet 

 fever, measles, kala-azar, and hydrophobia. 



