Cell-Theory not Sufficient for Eocplaimncj Organism 187 



proliferate, otlier tissues of exactly the same kind. Nothing 

 concerning the minute structure of organic beings is better 

 established than that in general tissue cells are "true to 

 kind"; that is, once a muscle or nerve or gland cell, always a 

 muscle or nerve or gland cell, not only in the particular cell's 

 own existence but in its progeny also. Clearlv tliis must be 

 so. Were it not, the organism would really not be an organ- 

 ism at all ; it would be a riot of cells differentiated and un- 

 differentiated. 



So obviously and widely true is this that some biologists 

 have believed it deserves crystallization into a phrase com- 

 parable io\)m7ie vitmm ex vivo. Accoidinglv we have Vir- 

 chow's omnis cellula e cellida transformed by L. Bard into 

 omnis cellula e cellula ejusdem naturae. lUif were this for- 

 mulation rigidly true, and were the tissue elements absolutely 

 unmodifiable in their individual lives, the adult organism, at 

 least, would certainly be held in the grip, figuratively speak- 

 ing, of its cells, and the fact might be taken as evidence of the 

 weightiest kind in support of the theory that the cells are the 

 key to all organic phenomena. 



Much truth as there unquestionably is in this aphoristic 

 statement, researches of later years have produced conclusive 

 proof that it can stand only after receiving important modi- 

 fication. 



Looking at the problem of the deviation of the cells of an 

 organism from type in a broad way, though without presum- 

 ing to make the classification and discussion exhaustive, we 

 find that three rather well defined classes of such deviations 

 have been observed. There are (1) cases in which tissues are 

 induced to undergo radical and more or less pennanent 

 transformation by coming into close and long-continued 

 contact with new or differently applied influences of the 

 external world; (2) cases in which the re])lacement of lost 

 parts of an organism is effected through either the tlirect 

 transformation of tissue of one sort belonging to an intact 



