,6 THE BEGINNINGS OF LIFE. 



All that we have that is good and safe, as the steam- 

 engine, the electric telegraph, &c., witness to that 

 principle. It would require a perpetual motion, a fire 

 without heat, heat without a source, action without 

 reaction, cause without effect, or effect without a cause, 

 to displace it from its rank as a law of nature.' The 

 time, therefore, must come when the really funda- 

 mental doctrine of the persistence or indestructibility 

 of Force will be recognized by all educated persons 

 to have an equal validity with the secondary, though 

 more familiar, doctrine of the indestructibility of 

 Matter. The two doctrines are correlatives, and the 

 admission of one implies the truth of the other as a 

 necessary consequence. 



Having come to an understanding as to what views 

 we are to take of Force and of the mutual relations 

 of the several physical forces, we now have to enquire 

 as to the relation in which these stand to the so-called 

 c vital forces ' manifested by Living Organisms. 



The first real 1 step in explanation was taken in 



1 In an 'Inaugural Address,' delivered in 1868 at the Jeafferson 

 Medical College, U.S., by Dr. J. Aitken Meigs, he claims the credit for 

 Dr. Metcalfe of having initiated this part of the doctrine. These 

 claims, and also others concerning Lardner Vanuxem, have been con- 

 sidered in the 'British Medical Journal,' January 16, 1869, p. 50. Dr. 

 Metcalfe's work, published two years earlier, in 1843, was entitled, ' On 

 Caloric ; its Mechanical, Chemical, and Vital Agencies in the Pheno- 

 mena of Nature.' Dr. Metcalfe seems to have been a man of much 

 power and originality, though he still looked upon heat as a material 

 substance, an elastic fluid named caloric. This view, of course, vitiates 

 his treatment of the subject, though it seems clear, from the passage 



