126 Mr. W. F. Stanley. 



From the experiment of Prof. Tait, just given, we find that 

 a smoke ring is projected from the smoke chest for a consider- 

 able distance in the air by a sudden impulse upon the stretched 

 canvass which forms the back of the chest ; whereas the con- 

 tinuity of the impulse for a longer time, so that it becomes a 

 pressure, projects the smoke for a short distance only. From 

 this we may conclude that impulsive impressions are the 

 most highly projectile ; therefore, assuming that this principle 

 applies also to the circulatory system of an animal, we see 

 the reason why the heart of all animals should act by pul- 

 sation and not by simple alternate pressures, which would not 

 diffuse the blood in the same manner. 



If we minutely examine the action of the heart, which we 

 may readily do in many of the lower animals, as in daphnia, 

 or the common snail, or better still by dissection of a live 

 mussel or oyster, we shall see that the opening of the valves 

 is relatively slow, whereas the closing is impulsive. The same 

 form of action is also clearly felt in the motion of the human 

 pulse ; therefore it is only in the smaller blood-vessels that this 

 impulsive action of the heart is lost, or is left only slightly 

 evident, as may be seen in the circulation of blood in the frog's 

 foot or fish's tail, where the pulsatory motion is nearly exhausted. 

 In the same manner it may be observed in the breath issuing 

 from the mouth and nose, that the vitiated fluid we exhale, 

 which it is necessary should be projected to such a distance as 

 not to be again inhaled, is ejected b)' a more sudden and 

 powerful action of the lungs than the reverse action of inhal- 

 ation ; this we may particularly notice under great exertion 

 when breath is thrown out with the greatest vigour, and 

 panting, as it is termed, occurs. 



In the next place we may notice that the impulsive action 

 producing the vortex form of motion throws the current lines 

 of a moving fluid outwards, and therefore the lateral openings 

 in a central artery, which take certain directions, do not neces- 

 sarily in taking this direction produce a very frictional form of 

 motion in the fluid which enters them. This is a very import- 

 ant point in animal economy. Thus, assuming that a current 

 running down an artery has to enter a lateral orifice, the vortex 

 direction will already be that which will assist the entry.* 



Considering again our original form of vortex motion, as 

 shewn in a former experiment, we find as a principle that a 

 unit projection has a natural tendency to separation from a 

 centre, and if the area of motion be reduced to a plane in any 

 way by side resistance, a simple current will have on projec- 

 tion a constant tendency to move outwards from the axis of 



*Mr. Stanley was able to illustrate this very clearly by experiment. 



