May 14, 1915] 



SCIENCE 



711 



fat globules instead of with glycogen. He 

 also found that in the Cladocera "the pe- 

 riod of active growth is accompanied by 

 glycogen — as opposed to fat — ^metabolism. ' ' 

 He observed, moreover, that if Cladocera 

 are crowded at a low temperature the fat 

 metabolism (with inhibition to growth) is 

 favored, while at high temperatures and 

 with no crowding of indiAriduals the gly- 

 cogen metabolism is favored. In the latter 

 case a purely parthenogenetic mode of 

 propagation is observed, while in the former 

 sexual reproduction takes place. The effect 

 of crowding of individuals is apparently 

 due to products of excretion, which then 

 act on growth and reproduction indirectly 

 by modifying the "glycogen metabolism" 

 to "fat metabolism." 



Factors which directly inhibit growth 

 have been discovered by Jas. B. Murphy, 

 of the Eockefeller Institute. It was known 

 that tissues can not be successfully trans- 

 planted into a different species. Murphy 

 discovered that this rule does not hold for 

 the chick embryo. Any kind of tissue, even 

 human, will grow if transplanted to such 

 an embryo. This growth of the trans- 

 planted tissue will stop, however, when the 

 chick is ready to hatch, and Murphy found 

 that this is due to the development of a 

 certain type of cells in the chick embryo 

 at that period, namely, the lymphocytes. 

 Murphy found, moreover, that he could 

 put adult mice and rats also into the con- 

 dition of tolerance to foreign tissues when 

 he destroyed their lymphocytes by an ex- 

 posure to X-rays. As soon as the lympho- 

 cytes are formed again foreign tissues can 

 not grow any longer on the animal. In this 

 case we have a definite inhibition of growth 

 by the action of lymphocytes which collect 

 around the transplanted piece. It is not 

 yet possible to state to what extent this 



observation on the inhibition of growth can 

 be generalized. 



"We shall see later that possibly the oppo- 

 site may also be true, namely, that certain 

 cellular elements may have an accelerating 

 effect on growth. 



"When a wound is made, cells which had 

 been at rest may begin to grow. In many 

 lower animal organisms and in plants whole 

 organs may be induced to grow as a con- 

 sequence of a mutilation. These phenom- 

 ena are known under the name of regenera- 

 tion. The name indicates the power of a 

 living organism of restoring lost parts. 



"We can see from a physicochemical view- 

 point why a cell should be endowed with 

 a power of growing indefinitely, since we 

 only need to assume the presence of suitable 

 synthetic enzymes in the cell; but we fail 

 to see from the same viewpoint why an 

 organism should have the power of restor- 

 ing lost parts. "Weismann and others have 

 tried to account for this power in a meta- 

 physical way which was shown to be in 

 conflict with the facts. 



The statement that regeneration consists 

 in the restoration of lost parts is not always 

 the exact expression of the actual facts. In 

 plants, e. g., we notice — in the majority of 

 cases — not a restoration of the lost parts 

 but the otitgrowth of one or more dormant 

 buds which are often at some distance from 

 the seat of injury. There has been some 

 discussion whether in view of this fact we 

 can say that regeneration exists in plants. 

 This merely verbal difficulty disappears if 

 we disregard the metaphysical sense of the 

 term regeneration and realize that the es- 

 sential feature of the phenomenon is the 

 fact that if we wound living organisms, 

 cells or anlagen which had ceased to grow 

 suddenly begin to grow. Thus the problem 

 of regeneration becomes a problem of 



