<Z CROONIAN LECTTJEES 



mechanical work done in a given time, and 

 they translate it into its equivalent of heat, 

 weighing also the urea produced in that time. 

 By burning a known weight of muscle out of 

 the body, they determine how much heat it 

 can produce ; and from this they can calculate 

 how much muscle must be burnt in the body to 

 give an amount of heat equivalent to the 

 mechanical work done in the given time. 

 They then calculate what amount of urea this 

 weight of muscle would produce. By com- 

 paring the actual amount of urea produced with 

 the calculated amount, it appears that only 

 one-fifth of the work can come from chemical 

 change in the nitrogenous texture of the 

 muscles. Four-fifths of the work must arise 

 from the chemical action going on in the non- 

 nitrogenous matters in the muscles or in the 

 surrounding blood. 



The experiments made by Dr. Parkes most 

 completely confirm the view that the motion of 

 the muscle during exercise does not bear any 

 relationship to the amount of chemical disinte- 

 gration in the albuminous substance of the 

 muscle. Indeed, he suggests the opinion that 

 the action of the muscle is not connected with 



