MOTION IN THE ANIMAi, ORGANISM. 



01 



nomena occur when the temperature is once appears as the cause of change oi 



lowered to a certain extent. 



The phenomena of vitality in a living or- 

 ganism diminish in intensity when heat is 

 abstracted, provided jthe lost heat be not re- 

 stored by other causes. 



Deprivation of food soon puts a stop to 

 all manifestations of vitality. 



The contact of the living tissues with the 

 elements of nutrition is determined in the 

 animal body by a mechanical force produced 

 within the body, which gives to certain or- 

 gans the power of causing change of place, 

 of producing motion, and of overcoming 

 mechanical resistance. 



We may communicate motion to a body 

 at rest by means of a number of forces, very 

 different in their manifestations. Thus, a 

 time-piece may be set in motion by a falling 

 weight, (gravitation,) or by a bent spring 

 (elasticity.) Every kind of motion may be 

 produced by the electric or magnetic force, 

 as well as by chemical attraction; while we 

 cannot say, as long as we only consider the 

 manifestation of these forces in the pheno- 

 menon or result produced, which of these 

 various causes of change of place has set 

 the body in motion. 



In the animal organism we are acquainted 

 with only one cause of motion ; and this is 

 the same cause which determines the growth 

 of living tissues, and gives them the power 

 of resistance to external agencies ; it is the 

 vital force. 



In order to attain a clear conception of 

 these manifestations of the vital force, so 

 different in form, we must bear in mind, 

 that every known force is recognized by two 

 conditions of activity, entirely different in 

 the phenomena they offer to the attention 

 of the observer. time alone, but to the pressure multiplied 



The force of gravitation inherent in the into the time', which is called the momentum 

 particles of a stone, gives to them a con- ! of force. 

 tinual tendency to move towards the centre ' 

 of the earth. 



This effect of gravitation becomes inap- 



place in the stone, which acquires motion, 

 or falls. Resistance is invariably the result 

 of a force in action. 



According as the stone is allowed to falJ 

 during a longer or shorter time, it acquires 

 properties which it had not while at rest ; it 

 acquires, for example, the power of over- 

 coming more feeble or more powerful obsta- 

 cles, or that of communicating motion to 

 bodies in a state of rest. 



If it fall from a certain height it makes a 

 permanent impression on the spot on which 

 it falls ; if it fall from a still greater height 

 (during a longer time) it perforates the table ; 

 its own motion is communicated to a certain 

 number of the particles of the wood which 

 now fall along with the stone itself. The 

 stone, while at rest, possessed none of these 

 properties. 



The velocity of the falling body is always 

 the effect of the moving force, and is, ceteris 

 paribus, proportional to the force of gravi- 

 tation. 



A body, falling freely, acquires at the end 

 of one second a velocity of 30 feet. The 

 same body, if falling on the moon, would 

 acquire in one second only a velocity of 

 sWh of a foot=l inch, because in the moon 

 the intensity of gravitation (the pressure 

 acting on the body, the moving power) is 

 360 times smaller. 



If the pressure continue uniform, the ve- 

 locity is directly proportional to it ; so that, 

 for example, the body falling 360 times 

 slower, will, after 360 seconds, have the 

 same velocity as the other body after one 

 second. 



Consequently, the effect is proportional, 

 not to the moving force alone, nor to the 



resses 

 er the 



In two equal masses the velocity exp 

 the momentum of force. But unck 

 same pressure a body moves moie slowly 



preciable to the senses when the stone, for I as its mass is greater ; a mass twice as great 

 example, rests upon a table, the particles of | requires, in order to attain in the same time 



an equal velocity, twice the pressure; or, 

 under the single pressure, it must continue 

 in motion twice as long. 



In order, therefore, to have an expression 

 for the whole effect produced, we must mul- 

 tiply the mass into the velocity. This pro- 

 duct is called the amount of motion. 



The amount of motion in a given body 

 must in all cases correspond exactly to the 

 momentum of force. 



These two, the amount of motion and the 

 momentum of force, are also called simply 

 fvrce; because we suppose that a less pres- 

 sure acting, for example, during 10 seconds, 

 is equal to a pressure ten times greater, act- 

 ing only during one second. 



The momentum of motion in mechanics 

 signifies the effect of a moving force, with- 



which oppose a resistance to the manifesta- 

 tion of its gravitation. The force of gravity, 

 however, is constantly present, and mani- 

 fests itself as a pressure on the supporting 

 body ; but the stone remains at rest ; it has 

 no motion. The manifestation of gravity in 

 the state of rest we call its weight. 



That which prevents the stone from falling 

 is a resistance produced by the force of at- 

 traction, by which the particles of the wood 

 cohere together ; a mass of water would not 

 prevent the fall of the stone. 



If the force which impelled the mass of 

 the stone towards the centre of the earth 

 were greater than the force of cohesion in 

 the particles of the wood, the latter would 

 be overcome : it would be unable to prevent 

 the fall of the stone. 



When we remove the support, and with 



out reference to the time 



in which 



(velocity) ii 

 If one man, for example, 



it the force which has prevented the mani- it was manifested. 



festation of the. force of gravity, the latter at , raises 30 Ibs. to a height of 100 feet, and a se 



