GENERAL PHYSIOLOGY 197 



Amoeba riridis, Vorticella Tiridis and Radiolaria etc.), and it is 

 conceivable that some gut-dwelling forms may perform a useful 

 activity for a host by disposing of pernicious bacteria, or by pre- 

 paring food substances for use by the host as do Hypermastigidfe 

 in termites (Cleveland). Commensals, such as Endamoeha coli, 

 Endamoeba nana, Trichomonas species and other intestinal forms 

 may, on occasions, turn into parasites, as is the case with Tricho- 

 monas (Tritrichomonas,l\ohnd), Giardia (Lamhlia), etc. Musgrave 

 and Clegg, indeed, are skeptical of any amoeba that may get into 

 the intestine, taking the view that any free-living form capable of 

 adapting itself to conditions of a digestive tract, may adapt itself 

 to a mode of life injurious to the host. 



Parasites upon reaching a site where the environmental conditions 

 of food, etc., are suitable, begin to multiply and to accumulate, 

 thus giving the appearance of selecting a given organ or tissue. In 

 this way, the organisms of smallpox {Cytoryctes varioIcB) are charac- 

 teristic parasites of the chorium; those of rabies (Neuroryctes 

 hydrojjhohioe) are nerve tissue parasites, while Plasmodium, Proteo- 

 soma, Lei-shmama, Tryparjosoma, etc., are typical parasites of the 

 blood and lymph; Coccidia are intracellular in A-arious tissues which 

 are specific for each type of parasite, the particular habitat in all 

 cases, depending on the food conditions and the physiological reac- 

 tions of the host. Such habitats have led to the designations of 

 parasites as coelozoic (lumen dwelling), enterozoic (gut dwelling), 

 histozoic (tissue dwelling), cjtozoic (intracellular), and hematozoic 

 (blood dwelling) forms. Many of them combine two or more of 

 these phases during the life cycle. Thus gregarines are cj'tozoic 

 in youth, and coelozoic later in life; some flagellates (Leishmania; 

 Trypanosoma), are hematozoic and cytozoic; others are enterozoic 

 and histozoic (Sarcocystis) , and some are coelozoic in one host and 

 hematozoic in another (malaria organisms). 



(c) Aidotrojjhic Nntrition.—I{eteTotroph\c nutrition of all animals 

 is possible only where organic foodstuffs are present and such food- 

 stuffs, in the final analysis, are manufactured by chlorophyll-bearing 

 plants. INIany Protozoa, particularly flagellates, are provided with 

 this manufacturing outfit which appears in t^TDical green chlorophyll 

 color in Euglenida and Phytomonadida. In many cases (Chryso- 

 monadida, Cryptomonadida), the green color is masked by yellow 

 or brown pigment which is easily dissolved in weak alcohol leaving 

 the green chlorophyll exposed; or the color ma^' be blue-green as in 

 the rhizopod Paulinella. Green chlorophyll resembles plant 

 chlorophyll in all respects— but yellow chlorophyll, especialh' the 

 phycopyrin of the Dinoflagellida, is closely similar to the yellow 

 coloring matter of diatoms (diatomin). In many cases {Euglena 

 sangninea, Hcemotococciis plurialis, and Chlamydomonas nivalis) the 

 green is masked by a red hematochrome termed karotin, which is 



