OTHER MODES OF FORCE. 159 



killed frogs absorb oxygen and exhale carbonic acid, and that 

 when they are thrown into a state of contraction, and still 

 more when they perform mechanical work, the absorption is 

 increased ; and he even calculates the equivalents of work so 

 performed. 



M. Beclard finds that the quantity of heat produced by 

 voluntary muscular contraction in man is greater when that con- 

 traction is what he terms static that is, when it produces no 

 external work, but is effort alone than when that effort and 

 contraction are employed dynamically, so as to raise a weight 

 or produce mechanical work. Every year is now adding evi- 

 dence that the forces brought into play by organised beings are 

 traceable to the continuous and mainly to the chemical effects 

 of food, air, light, &c. The assimilation of carbon by plants, 

 that of carbon and nitrogen by animals, together with the 

 slow combustion by inhalation of oxygen ; and the derivation 

 of the forces which animate and keep alive organisms, from 

 the heat and light radiated by the sun, are now becoming 

 accepted beliefs. 



Thus, though we may see no present promise of being able 

 to resolve sensations into their ultimate elements, or to trace, 

 physically, the link which unites volition with exertion or 

 effort, we may hope to approximate the solution of these 

 deeply interesting questions. 



In the same individual the chemical and physical state of 

 the secretions in the warm may be compared with those in 

 the cold parts of the body. The changes in digestion and 

 respiration, when the body is in a state of rest, may be com- 

 pared with those which obtain when it is in a state of activity. 

 The relations with external matter, maintaining, by the con- 

 stant play of natural forces, the vital nucleus, or the organisa- 

 tion by means of which matter and force receive, for a definite 

 period, a definite incorporation and direction, may be ascer- 

 tained, while the more minute structural changes are revealed 

 to us by the ever-improving powers of the microscope ; and 

 thus step by step we may learn that which it is given to us to 

 learn, boundless in its range and infinite in its progress, and 

 therefore never giving a response to the ultimate Why ? 



As the first glimpse of a new star is caught by the eye of 



