NUTRITION. 249 



ing to some very acute writers d , these, when once formed and 

 perfected, remain invariably entire. 



** There can be no doubt that some of the similar solids, v. c. 

 the epidermis and nails, are gradually destroyed and renewed ; 

 the same is proved by the frequently surprising attenuation of 

 the flat bones, especially of the skull, from defective nutrition, 

 in old age e ; and" some imagine " it is proved also by the well- 

 known experiment of dyeing them, in warm-blooded animals, with 

 madder root." 



But the redness imparted to the bones by feeding animals with 

 madder, does not prove that the matter of the bones is constantly 

 changing ; because the opinion that the madder unites with the 

 phosphate of lime in the blood, and thus reddens all the bony 

 matter subsequently deposited, is erroneous. Mr. Gibson proved, 

 by numerous experiments, that the serum has a stronger affinity 

 than the phosphate of lime, for madder, The serum being 

 charged with madder, the phosphate of lime of the bones, al- 

 ready formed, seizes the superabundant madder, and becomes 

 red. If the madder is no longer given to the animal, as it is con- 

 tinually passing off with the excretions, the stronger attraction of 

 the serum draws it from the bones, and they re-acquire their 

 whiteness. f The attenuation of the flat bones shows, I imagine, 

 wasting only. 



The constant renewal of the epidermis is demonstrated by 

 wearing black silk stockings next the skin. The microscope 

 exhibits that very minute fragments are incessantly thrown off 

 from the mucous membranes no less than from the skin.* 

 That the hair and nails not only grow perpetually, but are even 

 reproduced, is certain from the great quantity of the former 

 which falls off the head whole if worn long, while a good head of 

 hair still continues; and from the renewal of the latter, after the 

 loss of a great part of a finger. I once attended a middle-aged 

 woman in St. Thomas's Hospital, who had lost nearly the whole 

 of the first phalanx of a finger, and yet the stump was tipped by 



d " See J. Chr. Kemme, Beurtheilung eines Beweises vor die Immaterialitat der 

 Seele aus der Medecin. Halle. 1776. 8vo. 



And his Zweifel und Erinnerungen wider die Lehre der Aerzte von der Erridh- 

 rung derfesten Theile. Ibid. 1778. 8vo." 



e " Respecting this mutability of the bones, I have spoken at some length in 

 my osteological work, ed. 2. p. 26. and elsewhere." 



f Manchester Memoirt, vol. i. g Raspail, 1. c. pp. 245. 505. 



