176 CYTOPLASMIC INCLUSIONS 



divide inside the gastriole to form a larger number of small granules, 

 and both the mitochondria and the intermediate lipoid bodies (endoplas- 

 mic Golgi) fracture and split into rods as the granule within the sphere 

 grows; yet in none of these cases is the division more than an incident 

 in the cycle of the original granule, which arises in all cases de novo. The 

 division of cytoplasmic granules is merely an indication that the granule 

 is unstable under the particular conditions of size, surface tension, and 

 so forth. 



The term "vacuolar reaction" was introduced by Volkonsky to de- 

 scribe the relationship between the formation of new digestive granules 

 (his vacuome) and the presence of food. The pattern of the reaction 

 depended both upon the species of cell and upon the type of food present. 

 This formation of granules as a response to a specific stimulus is by no 

 means restricted to the single case of the digestive granules. The forma- 

 tion of secretion granules in the Tintinnidae is a specific response to the 

 factors which require a new lorica, and these granules are present at no 

 other time. The formation of the complex refractive bodies in Amoeba 

 is a specific response of that particular protozoon to excess food; when 

 this condition no longer holds, the granules are resorbed. The excre- 

 tory granules of Ichthyophthhius are the response of this protozoon to 

 the presence of metabolic wastes, which result from active feeding and 

 growth and which disappear in encystment, when the original condition 

 no longer holds good. The segregation bodies of Opalina likewise exhibit 

 changes which are specific responses to the particular food which is 

 available. Horning (1929) points out that the disappearance and re- 

 appearance of mitochondria in Monocystis is correlated with the decrease 

 and increase of metabolism resulting from encystment and excystment. 

 Volkonsky's vacuolar reaction is one case of general response, or "granu- 

 lar reaction," of the cell to a host of stimuli. If the stimulus is always 

 present, the particular granules which are characteristic for the stimulus 

 and for the particular cell under consideration are always present, but if 

 the stimulus is intermittent, the particular granules involved are present 

 only for the corresponding period. 



Continuity is of no significance in the evaluation of the granules, but 

 is rather a criterion of the continuity of the stimulus which induces the 

 formation of the granule. This, together with the demonstration that 

 the division of the granules is purely incidental, shows that it is not possi- 



