112 ORGANISM AND MECHANISM 



seems to be with the conservation of energy. An animal, 

 such as a dog, supposed for the sake of simplicity to be at 

 rest, takes in potential energy in the form of food, and takes 

 in oxygen to keep the vital combustion agoing. It uses up 

 the energy in internal activities : the heart drives the blood 

 round the body, the midriff rises and falls, the lungs empty 

 and fill, and so on. Now, if we allow for the potential 

 energy of waste-products and storage-products, we find that 

 the heat given off is in accurate correspondence with the 

 energy taken in. The accounts balance. The invention 

 known as a calorimeter made it possible for Rubner to dem- 

 onstrate that the heat-energy given off by an animal during 

 a prolonged experiment was the equivalent of the food taken 

 in, with a discrepancy of only 0.5 per cent, which is believed 

 to be the all but inevitable discrepancy due to the conditions 

 of experiment. There was a smaller discrepancy (0.1 per 

 cent.) in Atwater's experiment of sixty-six days during 

 which his students worked in a calorimeter. When they re- 

 mained at rest, the discrepancy disappeared. It is plain, 

 then, that the living of the animal is in general accordance 

 with the big generalisation that the sum total of energy 

 in a closed system remains constant. One mode may change 

 into another mode, but no energy ceases or is lost in the 

 transformation. 



It is certain that a chemical and physical description 

 can be given of much that goes on in organisms, and this 

 kind of description will certainly extend its scope. We need 

 only refer to Professor Bayliss's Principles of Physiology 

 as a fine illustration of the application of chemical and 

 physical analysis to the activities of the living body, and to 

 Professor D'Arcy Thompson's Growth and Form as its 

 counterpart in the domain of morphology. At the same time 



