GENERAL PHYSIOLOGY 203 



is well illustrated by the harmonious life of some chlorophyll-bearing 

 forms, Zoochlorella, Zooxanthella, etc., and Protozoa in which the 

 former live (Paramecium bursaria, "yellow cells of Radiolaria and 

 Foraminifera," Stentor viridis, Amoeba viridis, Vorticella viridis, 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 

 preparing food substances for use by the host as do Hypermastigidae 

 in termites (Cleveland). Commensals, such as Endamoeba coll, 

 Endamoeba nana, Trichomonas species and other intestinal forms 

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

 monas (Tritrichomonas, Kofoid), Giardia (Lamblia), etc. 



2. Products of Assimilation. — With the majority of forms the 

 products of assimilation vary with the type of food used and are 

 frequently so abundant in the cell as to give a characteristic appear- 

 ance or color to the animal. Thus the refringent granules of Pehmyxa 

 palustris (Stole.) produce a peculiar refringent effect. The brown 

 granules of Plasmodium, species, characteristic of malaria, are 

 products of hemoglobin assimilation. Similarly the coccidin of 

 Coccidia; stentorin of Stentor coeruleus and Folliculina ampulla; the 

 pink of Holosticha; the lavender of Blepharisma undulans or the 

 red of Mesodinium rubrum, are examples of the great variety of 

 colored cellular substances dependent upon the food that is eaten. 

 In the absence of the specific kinds of food which yield these chromic 

 products the organisms are colorless, and colored or colorless indi- 

 viduals of the same species may appear in the same culture (see 

 p. 134). 



