L56 



'HE CIBC1 LATION OP THE lU.ool. 



can be demonstrated l>\ observing the Mow through a wide tube of water in 

 which are suspended lycopodium spores. By placing in the tube small 

 In-ill tubes so arranged that one open end lies near the periphery and 

 die other near the center, it can be seen thai the differences in pressure 

 are such as to cause the fluid to Mow from periphery to axis (centripetal 

 eddies). 



If the benl tubes are used to study the conditions of flow in 8 tube which 

 suddenly becomes wider, it will be found thai where the wide portion 

 starts centripetal eddies are se1 up, which tend to carry the spores into 



I lie axis of the st renin, where their velocity [g greatly inere;ise(|. \ow 



these are the conditions obtaining ;ii the beginning of the large arteries 



S.a.-D.V. 



D.a.-S-v. 



Pig, Diagran liowing lh< position "I i he cardial chambei and valvi during |>rei !olc 



I '.v. ) and 'In nil pi I. I r'i om Landoi 



of the heart, the orifice into the ventricles being constricted, while al 

 the sinus valsalvae the vessels are dilated. A centripetal vortex must be 

 • I up in the sinus, tending to throw the valve flaps into ;i closed posi 

 lion, which, however is prevented by the Mood rushing between them 

 from the ventricles. They thus take up ;i mid position and vibrate in 

 the stream. When the efflux from the ventricle stops ;it the end of sys- 

 tole, the reflux, lasting for s nioinrni longer and being now unopposed, 

 immediately closes the valves, in which position they are then maintained 

 by the greater pressure on their upper surfaces. 



The position of I he \;d\es relative lo Ihr events of the c;irdi;ic cycle is 



show n in Pigs. 36 and 37. 



