CYTOPLASMIC INCLUSIONS 131 



rather than from the cytoplasm, a suggestion which later was proved to be 

 true, in the case of vacuole refractive bodies of A. proteus, by Mast 

 and Doyle (1935b). Volkonsky, however, checked his observations on 

 many ciliates and ruled out exogenous granules in the gastrioles of 

 Glaucoma by the use of bacterial free medium; he still observed diges- 

 tive granules in the vacuoles and was able to trace them from the cyto- 

 plasm. The migration of the digestive granules into the gastriole of 

 Ichthyophthirius was found by MacLennan (1936), but it was shown 

 that the granules do not penetrate any membrane. Instead, a new mem- 

 brane is formed (Fig. 31) around the whole gastriole and the inner 

 membrane, which is the original one, then disappears. The end result 

 is exactly the same as in the cases described by Volkonsky, but the 

 mechanism is somewhat different. 



Volkonsky's interpretation of the digestive granules as vacuome is 

 based upon their impregnation by the various Golgi-type methods. The 

 question as to the identification of the granules as shown by entirely 

 different methods is not present in this case, as it was in the case of the 

 scattered cytoplasmic granules (segregation granules), since the digestive 

 granules can be recognized independently of their staining reactions by 

 their relationship to the gastriole. Hall and Nigrelli (1937) claim that 

 the digestive granules are less consistent in impregnation than the 

 scattered cytoplasmic granules and dispute Volkonsky's claim that they 

 can be considered as vacuome. MacLennan (1940) showed that the 

 various types of osmiophilic granules could not be distinguished on the 

 basis of impregnation alone; in particular the digestive granules of 

 Ichthyophthirius show 100-percent impregnation. 



Few of the materials which occur in the digestive granules are known 

 from direct evidence. The digestive granules of Paramecium are high 

 in ash (MacLennan and Murer, 1934) and those in Ichthyophthirius 

 contain lipoids (MacLennan, 1936). These latter bits of information 

 are not as yet particularly useful and emphasize the need for more 

 specific knowledge. The presence of enzymes is suggested by the morpho- 

 logical evidence and this would be a fertile field for the use of the 

 microenzymatic methods. 



The digestive granules are not permanent self-perpetuating structures, 

 but appear to rise in the cytoplasm in response to the stimulus of feeding. 

 Volkonsky (1934) found that when the preexisting granules are utilized 



