146 THE RATE OF GROWTH [ch. 



from the beginning of growth, but from the comparatively late, 

 and unimportant, and even fallacious epoch of birth. A complete 

 curve of growth, starting from zero, has the same essential charac- 

 teristics as the regeneration curve. 



Indeed the more we consider the phenomenon of regeneration, 

 the more plainly does it shew itself to us as but a particular case 

 of the general phenomenon of growth*, following the same lines, 

 obeying the same laws, and merely started into activity by the 

 special stimulus, direct or indirect, caused by the infliction of a 

 wound. Neither more nor less than in other problems of physiology 

 are we called upon, in the case of regeneration, to indulge in 

 metaphysical speculation, or to dwell upon the beneficent purpose 

 which seemingly underlies this process of healing and restoration. 



It is a very general rule, though apparently not a universal 

 one, that regeneration tends to fall somewhat short of a complete 

 restoration of the lost part ; a certain percentage only of the lost 

 tissues is restored. This fact was well known to some of those 

 old investigators, who, like the Abbe Trembley and like Voltaire, 

 found a fascination in the study of artificial injury and the regenera- 

 tion which followed it. Sir John Graham Dalyell, for instance, 

 says, in the course of an admirable paragraph on regeneration I : 

 "The reproductive faculty... is not confined to one portion, but 

 may extend over many ; and it may ensue even in relation to the 

 regenerated portion more than once. Nevertheless, the faculty 

 gradually weakens, so that in general every successive regeneration 

 is smaller and more imperfect than the organisation preceding it ; 

 and at length it is exhausted." 



In certain minute animals, such as the Infusoria, in which the 

 capacity for "regeneration" is so great that the entire animal 

 may be restored from the merest fragment, it becomes of great 

 interest to discover whether there be some definite size at which 

 the fragment ceases to display this power. This question has 



* The experiments of Loeb on the growth of Tubulaiia in various saline 

 solutions, referred to on p. 125, might as well or better have been referred to under 

 the headmg of regeneration, as they were performed on cut pieces of the 7,oophji;e. 

 (Cf. Morgan, op. cii. p. 35.) 



"f Powers of the Creator, i, p. 7, 1851. See also Rare and Remarkable Animals, 

 II, pp. 17-19, 90, 1847. 



