GENERAL CONSIDERATIONS 39 



I regard it as probable, that the gradual deterioration of this important 

 organ of the ciliate cell, is the underlying cause of waning vitality and 

 ultimate death of protoplasm in isolation cultures (Fig. 10). 



With parasitic forms there is probably the same underlying variation 

 in vitality, but there is not the same possibility of measuring it, at least 

 not in any direct way. 



Remarkable as these phenomena are, they leave us cold so far as the 

 matter of protoplasmic vitality is concerned. The interpretations pre- 

 sented here are, after all, essentially mechanistic, and even with the 

 ciliates the phenomena described are by no means universal, while in 

 some groups of Protozoa they are not shown at all, or else only in a 

 vague and indefinite manner. In ciliates there is one organoid of the 

 cell, the micronucleus, which transcends all other structures of the cell, 

 and, although it is apparently not functional except in heredity and 

 activities connected therewith, such as regeneration, and so forth, it 

 does appear to be the most essential morphological element of the 

 fundamental organization. Its agent in metabolism is the macronucleus, 

 which is derived from it. For the secret of life and longevity in ciliates 

 we must turn to this inconspicuous and often overlooked structure of 

 the cell and of the cyst. 



In other groups of the Protozoa, the homologue of this important 

 element of the cell lies in the usually single nucleus. Furthermore, in 

 the micronucleus it is probably the chromatin content that gives it its 

 power; and, in other groups than the ciliates, it is the chromatin con- 

 tent that makes the nucleus what it is. The value and importance of 

 chromatin is seen by the meticulous care with which it is distributed 

 to daughter cells and to progeny generally, while the maturation divi- 

 sions bespeak its significance in heredity. The secret of life and vitality 

 must thus be sought not in the daily activities of living things, but in 

 that enigmatical substance — chromatin — which is about us in all living 

 things, including ourselves. That secret may never be disclosed. 



Literature Cited 

 Balbiani, G. 1859. Du role des organes geneateurs dans la division spent, des 



infusoires cilies. J. Physiol. Pathigen., Ill: 71-87. 

 1861. Recherches sur les phenomenes sexuelles des infusoires. J. Physiol. 



Pathigen., : 102-30, 194-220, 431-48, 465-520. 

 Barry, M. 1843. On fissiparous generation. Edinb. New phil. Jour., 35: 205- 



20. 



