50 HETAMOKPHOSES OF MAN 



The organs whose functions are discharged during 

 embryonic life do not all share the same fate. Some, 

 as the thymus, which is situate in the chest, and the 

 supra-renal capsules, are only arrested in their develop- 

 ment, and are found in the adult, although seemingly 

 without having any function to discharge : others 

 are still employed and engaged in some new occu- 

 pation. It is in this way that the vessels which are 

 connected with the nutrition of the foetal lungs are 

 enlarged to such an extent after birth, that all the 

 blood forced from the heart during a single con- 

 traction, can flow through them to the respiratory 

 organ. 



The important phenomena which are exhibited in* 

 the mammal from the first appearance of the germ, 

 till death takes place, may be stated as follows : 

 first, epigenesis ; then evolution of the simple or 

 complex type, formation, modification, progressive 

 development, arrest of development, atrophy, and 

 destruction, or appropriation of organs. All these 

 phenomena, therefore, imply that, continual mole- 

 cular currents are established in every portion of 

 the frame. 



If to this unavoidable conclusion we add the 

 general law applicable to all vertebrates, that there 

 exist in the embryo at the time of its most rapid 

 growth, as well as in the adult, important organs 

 which carry out of the body the worn-out materials, 

 the term vital current will then appear in the sense 

 we have employed it. It alone allows the performance 

 of the various actions we have detailed already. 

 Assuredly it is this which carries with it the materials 

 of which the new being will be built, which lays 



