690 



Regeneration 



epithelial wounds. Barfurth (1891) showed 

 a similar process in frog larvae, and Poynter 

 ('22) in chick embryos; Oppel ('12) traced 

 the movements of corneal epithelivim of the 

 cat, but missed completely the amoeboid 

 stage. Matsumoto ('18) repeated Oppel's 

 tissue culture experiments using intra vital 

 stain to trace the reaction and confirmed 

 Peters. Rose ('48) has reinvestigated the role 

 of the epidermis and returns to the older 

 idea of Godlewski that the blastema is 

 formed from differentiated epidermis. 



Muscle Tissues. Muscle does regenerate 

 from muscle remaining after injury. The 

 difficulty with reconstitution here seems to be 

 the infiltration of connective tissue which 

 prevents the slower muscle elements from 

 entering. It was formerly thought that myo- 

 fibrillae had no capacity for regeneration but 

 that the entire replacement was a fibrous con- 

 nective tissue. This is true for heart damage 

 late in life. 



Cartilage and Bone. Cartilage does not re- 

 generate readily in the higher vertebrates, 

 in which it is formed from perichondrium. 

 Bone regeneration is a complex process, de- 

 pending first upon the formation of cartilage 

 with the appearance of callus, then cartilage 

 and the chondroclasts, osteoblasts and osteo- 

 clasts, resulting in the typical bone recon- 

 stitution. The time required for complete 

 repair is variable and depends to a large 

 extent on calcium utilization. There is an 

 important line here between the vitamin 

 complex and other internal factors. 



The Gut. Desquamation is constantly oc- 

 curring from the entire alimentary mucosa, 

 probably greater in degree than that occur- 

 ring in the epidermis. There is a constant 

 and consistent replacement of the glandular 

 content of the salivary, esophageal, gastric 

 and intestinal regions. The proliferation of 

 the mucosa is not of the pronounced cyclic 

 type, but is a continuous process. When a 

 part of the gut is removed, the intestine re- 

 maining does not reconstitute the part. The 

 gut remains in its reduced condition. Flint 

 ('10) removed 80 per cent of the intestine in 

 dogs, with viability; in such cases the extent 

 of villation is markedly increased, and physio- 

 logical readjustment takes place by a com- 

 pensating hypertrophy of the villi which 

 makes possible an increase in the absorptive 

 area. Grant ('45) has experimentally re- 

 moved the epithelial cells of the gastric 

 mucosa and finds that the cells are replaced 

 within a few hours, provided that the under- 

 lying gland cells are not distturbed. 



Glands. There have been many studies on 



the regeneration of glands. Podwyssozki 

 (1881) studied the regeneration of liver in 

 the rabbit. The bile ducts give rise to liver 

 cells. The salivary glands and kidney have 

 also been studied. The kidney is an example 

 of compensating hypertrophy, but the re- 

 generative phase is in many cases a very 

 active one. 



In these three big classes of vertebrates, 

 there is by far more regeneration than one 

 would suspect in a superficial examination 

 of the field. Hyperplasia and compensatory 

 hypertrophy play an important part in these 

 forms. The repetitive type of regeneration 

 is a vital and probably one of the chief sur- 

 vival values of these forms. 



GENERAL HISTOLOGY 



The early studies on the histology of the 

 regenerative process interpreted it in the 

 light of embryonic development (Goette, 

 1879; Strasser, 1879). Barfurth (1891) was 

 the first to point out the wandering character 

 of the epithelial cells and their stretching 

 quality which covers the wound before ac- 

 tive cell divisions occur. At the same time 

 Peters (1885) showed that this same process 

 occurred after wounds of the cornea. Since 

 then it has been found frequently (Poynter 

 in chick embryos, and numerous individuals 

 working on amphibians). 



In the tail, regeneration is brought about 

 by a typical succession, each tissue regen- 

 erating its like. Nerve cord gives rise to 

 nerve cord, but the regenerated nerve cord 

 is frequently different from the original, as 

 are also the spinal ganglia and spinal nerves. 

 The situation is entirely different in the 

 limbs, and here we fortunately have ex- 

 cellent studies of Naville ('24), Bohmel 

 ('29) and Hellmich ('30). 



THE EYE AND LENS 



The experimental attack upon the eye and 

 its regenerative capacity goes back to Bonnet 

 and Bliunenbach, who recognized that a 

 large part of the eye could be regenerated 

 provided that a small portion remained after 

 the original operation. Colucci (1891) 

 showed that the lens regenerated from the 

 edge of the iris. This paper is a remarkably 

 well done piece of work which was com- 

 pletely neglected until brought to attention 

 by Emery (1897). The workers during the 

 intervening period, however, were moved 

 by the controversial points which were raised 

 by Gustav Wolff (1895). His paper stressed 



