ZOOLOGY. 257 



as a state of dynamic equilibrium a continual succession of waste 

 and repair ; the former being the consequence of every act of mind or 

 body, the latter the result of the various processes of nutrition carried 

 on during repose. In a human body weighing 140 Ibs. about a ton of 

 various matters, solid, liquid, and gaseous, are received and assimilated 

 during a year ; yet the body appears exactly the same. Some organs, 

 however, such as the teeth and hair, have a limited existence. This 

 may be compared to the metamorphoses of insects,. Life is maintained 

 in a normal state when demand and supply are perfectly adjusted, 

 consumption being ever proportional to the total energy exercised. A 

 seed of a plant is in a state of dormant vitality, which the hibernation 

 of certain animals closely resembles. The blood which we have in 

 three stages or conditions that of to-day in its perfect state, that of 

 yesterday in its used state, and that of to-morrow in its preparatory 

 stage is the important agent in the nutrition or repair of wasted tis- 

 sues. Its great organ, the heart, has also its due periods of work and 

 rest or repair. The same is the case with the organs of respiration. 

 In health an increased demand for power meets with increased supply. 

 Hence the large size of the muscles of the arm of a blacksmith, and 

 the greater development of the brain when- the mental power is raised 

 by education. The mutual sympathy existing between all the organs 

 of the body is maintained by means of the blood and the nervous 

 system ; and by the action of the nerves on the blood-vessels, the varied 

 phenomena of the countenance (pallor, blushing, &c.) are produced. 

 In conclusion, Mr. Savory proposed to reduce the seven ages of man 

 to three : Growth or development, when supply of nutrition to the 

 tissues exceeds the demand ; maturity, when the two are balanced ; 

 and decline, when supply fails short of the* demand, and decay ensues. 



NATURE OF THE VITAL FORCE. 



The following is an abstract of a discussion before the British As- 

 sociation, on the nature of the so-called " vital force." Dr. Daubeny 

 was quite ready to allow that the term " vital force" was conditional. 

 At the same time, he felt that some of the phenomena of plant-life 

 could not be explained by physical causes. Such, he thought, was 

 the power plants had of selecting one kind of food rather than another, 

 and the power the leaves possessed of decomposing carbonic acid. 

 Prof. Williamson expressed his conviction that the processes of life did 

 not depend on physical causes. There were always causes acting in the 

 life of plants and animals that no physical principles with which Ave 

 were acquainted could explain. He instanced the fact of a hydra 

 taking one of its own tentacles into its stomach with an animalcule. It 

 digested the animalcule, but its tentacle suffered no harm. Mineral 

 bodies were subject to no decay as organic bodies were ; and it was 

 this death that showed the existence of a departed vital force from the 

 dead plant or animal. Mr. Lubbock thought the danger of using the 

 term '-vital" force o-r principle was, thai; persons who employed it 

 thought it explained the phenomena, which in no instance was the 

 case. He thought that the death of marine animals in fresh water, 

 and of fresh-water animals in salt water, was an instance of how physi- 

 cal circumstances influenced life. Dr. Lankester said, that the terra 

 " vital force " had been used in various senses, and Dr. Daubenv onlv 

 22* ^ * 



