REGENERATION 



119 



correct, and may be expressed according to our theory by sav- 

 ing that the supplementary determinants which are present in a 

 passive condition in the cells, are prompted to become active bv 

 the stimulus. But if an articular cavity is exposed, a stimulus 

 is likewise produced, which must affect the cells of the articular 

 cartilage, and doubtless also those of the underlying bone or 

 periosteum. If, therefore, all the cells in this region were 

 capable of reproducing the missing bones, and if the exposure 

 of the articulation were the ordinary form of injury, these cells 

 would certainly be just as much adapted for and capable of 

 responding to this stimulus, by a formative growth, as would 

 those situated at the broken ends of a bone. But the disa}-ticn- 

 lation of a limb, or of a part of a limb, hardly ever takes place 

 in the natural conditions of life, atid therefore could not have been 

 provided for by the organism ; the respective cells of the exposed 

 articular cavity could not consequently have been supplied with 

 the supplementary determinants necessary for regeneration. 

 Hence these cells are incapable of reacting in an adequate 

 manner to the stimulus due to the disarticulation. 



In spite of all the facts already mentioned, it might still 

 appear doubtful whether regeneration really depends on a special 

 adaptation of the part in question, and whether it does not result 

 from the degree of organisation of the animal, or at any rate 

 from a. ^^//i?;-^/ regenerative force possessed by the entire organ- 

 ism. The following considerations must, however, I think, set 

 aside all doubts on the question. Physiological and pathologi- 

 cal regeneration obviously depend on the same causes, and often 

 pass one into the other, so that no real line of demarcation 

 can be drawn between them. We nevertheless find that in 

 those animals in which the power of regeneration is extremely 

 great physiologically, it is very slight pathologically. This 

 proves that a slight power of pathological regeneration cannot 

 possibly depend on a general regenerative force present within 

 the organism, but rather that this jiower can be provided in 

 those parts of the body which require a continual or periodic 

 regeneration : in other words, the regenerative power of a part 

 depends on adaptation. Let us take a few examples. It was 

 mentioned above that fishes are said to possess a very slight 

 ' general regenerative power," because they are unable to replace 

 lost external parts, especially such structures as fins. Neverthe- 

 less many fishes are provided with teeth which are verv liable to 



