CHAPTER LXIII. 

 THE INFUSORIA. 



Introduction and methods of examination. 

 Parasitic species, p. 830. 



THE Infusoria are Protozoa the bodies of which are wholly or in part covered 

 with motor appendages or cilia. They have a distinct ectoplasm and endo- 

 plasm, contractile fibres, contractile vacuoles, and a nucleus divided into 

 two parts (macronucleus and micronucleus). In addition they have a mouth, 

 a pharynx opening into the endoplasm and an anus which is only visible at 

 the moment of expulsion of the excreta. 



They multiply generally by transverse division. After several generations 

 have been produced by fission the individuals show a tendency to conjugate, 

 and after certain changes have taken place in the nucleus of the two con- 

 jugated individuals the latter separate and each may then become the parent 

 of a further generation of schizogonic elements. 



In the stools and outside the body cysts are produced : the animal loses 

 its cilia, becomes rounded and appears to consist of a dark central mass 

 surrounded by a clearer peripheral zone. The cyst is the latent form of the 

 organism which again becomes ciliated when conditions are favourable. 



Five species of Infusoria are known which occur as parasites in man. 



Methods of examination. The technique to be adopted is similar to that 

 described in the case of the Amoebae. For detailed study of their structure 

 it will be found useful to stain the Infusoria in the living state, either with a 

 solution of quinolein blue (which stains the granules of the endoplasm but 

 neither the nucleus nor the cilia) or with Bismarck brown (which stains the 

 vacuoles first then the protoplasm but leaves the nucleus unstained). Violet 

 dahlia or malachite green may be used for staining the nucleus. The 

 dyes should be dissolved in the fluid in which the Infusoria are living 

 (normal saline solution) and the solutions should be weak (about 1 in 

 10,000). 



For fixing the Infusoria, osmic acid gives the best results. The vapour 

 of the acid should be allowed to act on the slide on which the drop of water 

 containing the parasites is placed : or a drop of a 1 per cent, solution of 

 osmic acid may be placed on a cover-glass and inverted on to the water on 

 the slide. 



Tissues intended for histological examination should be fixed in Flemming's 

 solution or in 30 per cent, formalin : the methods of staining are the same 

 as for the Amoabae. 



