56 Structure and Classification of Micro-organisms 



The infusoria are actively motile through abundant fine 

 hair-like formations known as cilia. These, multitudinous 

 as they are, vibrate synchronously with an oar-like move- 

 ment, propelling the organisms forward or backward or mak- 

 ing them revolve with great rapidity. Independent cilia 

 not infrequently encircle the oral aperture, causing a vortex, 

 in which the minute structures upon which the creatures 

 feed are caught and carried into the body. 



Size. The protozoa show very great variation in size. 

 Some of the sporozoa form minute parasites of the red blood- 

 corpuscles or other cells of the vertebrates. The treponema 

 is so small that it can slowly find its way through the pores of 

 a Berkefeld filter. 



On the other hand, the sarcoporidium is so large that one 

 of its cysts, composed of a single organism, can be seen with 

 the naked eye. Certain protozoa that play no part in morbid 

 processes myxosporidia and so do not come within the 

 scope of this work, may be several centimeters in diameter. 



Reproduction. The reproduction of the protozoa takes 

 place both asexually and sexually. It may be that there are 

 no strictly asexual protozoa, nearly all forms having been 

 shown upon intimate acquaintance to be subject to occasional 

 conjugation. Conjugation may result in the loss of individual 

 identity or the conjugated individuals may again separate. 



Whether the reproduction takes place asexually without 

 conjugation or sexually after conjugation, it always occurs by 

 division, 'which may be simple and binary or complex and 

 multiple. 



Wherever a distinct nucleus can be found, the multipli- 

 cation of the protozoa is preceded by some kind of mitotic 

 change. The more complex the structure of the nucleus, the 

 more complicated and perfect the mitosis. 



The elongate protozoa divide lengthwise, which is some- 

 times contrary to expectation, as in the cases of treponema 

 and spirochaeta. 



The multitudinous sporozoi'tes into which the zygotes of 

 the sporozoa divide are commonly the result of anterior divi- 

 sion into intermediate bodies known as oocysts, ookinetes, 

 sporocysts, etc. The nuclear substance is first divided so as 

 to be uniformly distributed among these, then further divided 

 so that some of it reaches each sporozoite. 



In the process of sporulation the entire parent may be 

 used up, as in the coccidium and plasmodium, or the parent 



