METABOLISM 263 



even died before the carbohydrate stores were exhausted (Tartar, 

 1959a). 



All these findings merely confirm that stentors, like other 

 organisms, are able to continue living for some time by consuming 

 nutrient reserves or their own vital substance during periods of 

 starvation. More precise studies of starving cells might dissociate 

 factors most dependent for their maintenance on continuous inflow 

 of new materials, or starving protozoa may prove particularly 

 sensitive and discriminatory in their response to specific additives 

 such as certain amino acids, in contrast to well-fed cells. At present, 

 one is above all impressed by the adaptive morphological changes 

 whereby starving ciliates become not merely shrunken but re- 

 formed on a smaller scale, as tiny but perfectly formed dwarfs are 

 produced. 



2. Storage and utilization of nutrient reserves 



Visible reserves in Stentor take the form of glycogenoid granules 

 and fat droplets. The first can be demonstrated by dark-field 

 illumination or Lugol's iodine stain and the second by Sudan III. 

 These reserves were the subject of an extensive field and laboratory 

 study of Zhinkin (1930) on polymorphus, with incidental observa- 

 tions on coeruleiis. 



Carbohydrate reserves are present in the form of granules which 

 are concentrated toward the posterior pole. Clearly revealed by 

 Tyndall eflFect using side illumination against a dark background, 

 one can observe the precise location of these granules in living 

 coeruleus (Tartar, 1959a). In animals which have been cleared of 

 food vacuoles by withholding food organisms, these reserves are 

 seen to occupy a subcortical band, forward from the posterior pole 

 and discontinuous in the oral meridian (Fig. 73). This is the 

 regular and preferred location, though overstepped if the carbo- 

 hydrates are especially abundant. Soluble in hot water and staining 

 red with iodine, Zhinkin identified the granules as glycogen. 

 Weisz thought them suflftciently diflFerent to merit the name 

 paraglycogen. Fat stores are present in the form of tiny droplets 

 throughout the endoplasm. 



Zhinkin followed stentors through an annual cycle. The most 

 conspicuous changes were that, with decreasing temperature in the 

 autumn, the carbohydrate reserves increased; but when the ponds 



s 



