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SCIENCE 



[N. S. Vol. XXV. No. 639 



regeneration might have a common cause. 

 At any rate, self-repair distinguishes the 

 organism from the machine. If parts of a 

 machine yield to stress and the factors of 

 safety become exhausted, the machine 

 would surely break down, unless it is re- 

 paired by human hands, just as it is made 

 by human hands. As far as I know, no 

 machine has yet been invented which is 

 provided with devices for a continual self- 

 repair. In the living organism self-repair 

 is a wide-spread function of living tissues 

 and organs. It is a dormant force, a re- 

 serve force, which springs into immediate 

 activity as soon as any injury is inflicted. 

 It is a factor of safety peculiar to the 

 living organism. It manifests itself in the 

 forms of regeneration and hypertrophy of 

 tissues and organs, and also in the func- 

 tional forms of inflammatory reaction, of 

 substitution, vicariation and adaptation. 

 And here it is interesting to observe that 

 self-repair does not set in only when the 

 margin of safety is exhausted, when there 

 is an actual need for repair, but already 

 when only the integrity of the factors of 

 safety is encroached upon. Self-repair is 

 a factor of safety also for the protection 

 of the factors of safety. When, for in- 

 stance, one kidney is removed, the hyper- 

 trophy of the secreting elements begins a 

 few hours later, although the urinary secre- 

 tion was hardly impaired. It is an attempt 

 to reprovide with luxurious tissue. The 

 liver cells regenerate, the thyroid, the ad- 

 renals and other organs hypertrophy and 

 regenerate even when the preceding injury 

 was not extensive enough to affect the func- 

 tion of these organs. It is, as stated before, 

 an attempt to restore the factors of safety. 

 A heart working above normal becomes 

 hypertrophied even if it has not yet met 

 with any obstacles ; it is a provision in time 

 against possible shortcomings ; it is a repair 

 of the factors of safety. This is a very in- 



teresting field, but it would lead us too 

 far to enter upon a detailed discussion of 

 the various aspects of the subject. We 

 would only call attention to two exceptions. 

 One is the very scanty repair which takes 

 place in the organs of reproduction. But 

 the affluence is here so immense that the 

 organs may safely forego tha benefits of 

 self-repair. The other exception concerns 

 the nerve ganglia ; nerve cells as a whole do 

 not regenerate. We have learned above 

 that the ganglionic masses of the central 

 nervous system are scantily provided with 

 factors of safety. Here we learn that they 

 are also deprived of the great aid afforded 

 by regeneration. There is some functional 

 self-repair in the central nervous system. 

 Other centers assume the work of the lost 

 ones; adjacent tissues become educated to 

 the work; dormant centers of the opposite 

 hemispheres wake gradually up to their 

 new missions. But all these substitutes are 

 insufficient satisfactorily to replace the lost 

 function, not to speak of a provision for 

 factors of safety. 



Here we must recall that the lack of 

 regeneration applies only to the nerve cells. 

 The nerve fibers, on the other hand, espe- 

 cially those of the peripheral nerves, show 

 rather a very active regeneration. 



The foregoing review shows, I believe, 

 conclusively, that the tissues and organs 

 of the living animal organism are abun- 

 dantly provided with factors of safety. 

 The active tissues of most of the organs 

 exceed greatly what is needed for the nor- 

 mal function of these organs. In some 

 organs the surplus amounts to five, ten or 

 even fifteen times the quantity represent- 

 ing the actual requirement. In the organs 

 of reproduction the superabundance and 

 waste of tissue for the sake of assuring the 

 success of the function is marvelous. 

 Furthermore, the potential energies with 

 which some organs, like the heart, dia- 



