CYTOLOGY 321 



Similarly, it was first shown by Rogers (1904) that the leishmania forms 

 of the parasites of kala-azar were in reality flagellates by their develop- 

 ment into leptomonas forms in culture. 



It is probable that the transformation which occurs in culture is an 

 imitation of that which takes place in the invertebrate host. 



In this description, wherever the words leishmania, leptomonas, cri- 

 thidia, or trypanosome are employed in an adjectival sense, they refer 

 to stages in the development of any of the flagellates which show these 

 particular forms, and are not used in a generic sense. When they are 

 employed as nouns, they refer to a member of the particular genus. Thus 

 one may speak of a leishmania form of a trypanosome, a trypanosome 

 form of a herpetomonas, or a leptomonas form of a leishmania. 



CYTOLOGY OF TRYPANOSOMES AND THE ALLIED FLAGELLATES. 



Before describing the individual genera, it will be necessary to consider 

 the structure and method of multiplication in greater detail. The whole 

 group shows a marked uniformity of minute structure, though, as will be 

 seen, considerable variation occurs in the actual size and shape of the body, 

 especially amongst the trypanosomes. 



CYTOPLASM.— The body is covered by the periplast, and within it 

 the cytoplasm is generally perfectly clear and of a very fine alveolar struc- 

 ture. Vacuoles may be present, especially the one already referred to, 

 which is near the kinetoplast. It has been described as contractile in 

 Herpetomonas tnuscarum, but this is probably incorrect. Occasionally, 

 forms with a highly vacuolated cytoplasm are seen, but these are abnormal 

 or degenerating individuals. 



Apart from the periplast, the cytoplasm is of uniform consistency, 

 and shows no differentiation into ectoplasm and endoplasm. Immediately 

 below the periplast longitudinal fibres can sometimes be made out, 

 especially in some of the larger trypanosomes (Fig. 28, B). These are 

 generally supposed to be myonemes or contractile fibres. Minchin (1909, 

 1909a), who had observed them in the trypanosomes of the perch and eel, 

 was unable to distinguish them in the smaller Trypanosoma lewisi. 



GRANULES.— Various kinds of granule may be present in the cyto- 

 plasm, especially anterior to the nucleus. Some of these may take a red 

 or purple tint with Romanowsky staining. In T. lewisi, Minchin (1909a) 

 refers to them as " chromatoid granules," and many writers have con- 

 sidered them to be volutin. On account of their affinity for certain 

 chromatin stains, they have sometimes been mistaken for nuclei. 



Flagellates of this group are sometimes packed with these granules, 

 but their presence seems to depend upon the rate of metabolism. The 



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