THE BEGINNINGS OF LIFE. 79 



this analogy. He observed that, if in a solution of nitre 

 and sulphate of soda a crystal of nitre be dropped, all 

 the dissolved nitre crystallizes, the sulphate remaining 

 in solution; whereas, on reversing the experiment, a 

 crystal of sulphate of soda is foim to crystallize all the 

 dissolved sulphate, leaving the nitre undisturbed. In 

 like manner, muscle selects from the blood its own 

 materials, which are there in solution, rejecting those 

 which the nerve will select.' And, in fact, the more 

 we study the phenomena of nutrition, growth, and 

 repair wheresoever taking place the more we may 

 become convinced of the fact that the influence of pre- 

 existing living matter does, in the main, show itself 

 in this way. It may be seen by the mode in which 

 an ulcer heals. The new skin forms, under ordinary 

 circumstances, only at the edges of the sore in 

 continuation with pre-existing skin; and the method 

 recently adopted by surgeons, of transferring a small 

 portion of epidermis to the midst of a large surface 

 which has been denuded by a burn, is but a practical 

 application of this physiological fact 1 . From the 



1 This admirable method of treatment was initiated by M. Reverdin, 

 of Paris, and first practised in this country by Mr. Pollock. The latter 

 says : ' It has appeared to me that when this process of cicatrization 

 approaches the margin of the original ulcer, although this may have been 

 indolent or stationary, there is a stimulus given to the latter, and a fresh 

 process of cicatrization commences from this edge, and new tissue is 

 formed in a direction to meet that from the transplanted portion. It has 

 also appeared to me that the process of cicatrization is more rapid in the 

 transplanted portion on the side nearest the edge of the original sore, when 

 the two edges approach each other.' (' Trans, of Clinical Society,' vol. iv.) 



