996 SPECIAL PHYSIOLOGY. 



REPARATION. 



The process by which injured or lost parts of the body are repaired 

 or reproduced, so that similar tissues are, after a time, developed in 

 their place, is known as regeneration or reparation. The formative 

 power is here the same as that by which the embryo is first developed, 

 and the developmental processes concerned are but extensions of those 

 retained in mature life. This process of regeneration is most active 

 during the earlier periods of existence. Thus, in cases of so-called 

 spontaneous amputation occurring to the foetus in utero, from constric- 

 tion by the umbilical cord, fingers have been afterwards developed on 

 the remaining portion of the limb. Instances, too, have been recorded, 

 in which almost as remarkable re-formations of lost parts have oc- 

 curred in infants, and even in children. In the same mariner, the 

 capacity of repair gradually diminishes as life advances, lost parts 

 which, in early life, are regenerated, being afterwards imperfectly 

 and incompletely reformed. Hence, in a child, the reparation of an 

 injury may easily take place ; whereas, in old age a similar lesion will 

 remain unrepaired. Experiments have shown that the vigor and 

 celerity of the repair of fractures, and the union of tendons in Mam- 

 malia, are in an inverse proportion to the age of the animal. (Paget.) 



Amongst the lowest animals, the process of reparation after injury is iden- 

 tical with the process of reproduction by gemmation or fission. If the hydra 

 be cut up into a number of small pieces, each of these becomes developed into 

 a perfect hydra, and this process can be repeated, over and over again, with a 

 similar result. The Annuloida likewise possess very great reparative powers; 

 thus it has been noticed that the holothurida, when pulled about or injured, 

 expel the whole of their viscera; after a few months, these are regenerated. 

 Amongst the higher Non-vertebrate animals, however, in which reproduction 

 by gemmation or fission does not occur, the power of reproducing a perfect 

 body from a fragment does not exist. The Crustacea and Arachnida can, 

 when fully developed, reproduce limbs and antennae. In the Myriapoda, on 

 the other hand, the reparative power ceases when they have reached their full 

 development; whereas, previously to this, antennae and limbs may be repro- 

 duced. The larvae of Insects are endowed with like powers of reproduction; 

 but the perfect Insects, at least the higher ones, have no such regenerative 

 power. Hence, it appears that the amount of reparative power is in an in- 

 verse ratio to that of the development through which the animal has passed 

 in its attainment of perfection. (Paget.) The reproductive power of the Mol- 

 lusca has not been much investigated; it is said that the common snail can 

 reproduce the head, if the cerebral ganglion be preserved. Amongst the Yer- 

 tebrata, the Amphibia possess very great reparative power. After excision 

 of an eye from the triton, or newt, a new one, it is said, may be developed in 

 its place, and the reproduction of an entire limb, or of the tail, occurs readily 

 in them. 



But in Man and the Warm-blooded animals, the true reparative 

 process is much more limited, being confined strictly to the reproduc- 

 tion of certain tissues. 



In the first place, there are several parts, such as the epidermoid and 

 epithelial tissues, and also the red corpuscles of the blood, which are 

 naturally undergoing constant reparation or decay, and are as con- 

 stantly being reproduced by what has been termed continuous growth, 

 or nutritive repetition. 



