MOVEMETS 7 T OF TI1E BLOOD IN THE VEINS. 355 



directly causes accumulation in the veins, will assist the heart in propelling 

 the blood into the arteries; and by the combined action of these two causes 

 is produced, among other effects, the rising and sinking of the Brain, syn- 

 chronously with expiration and inspiration, which are observed when a por- 

 tion of the cranium is removed. Several considerations, however, agree in 

 pointing to the conclusion, that no great efficacy can be rightly attributed 

 to the Respiratory movements as exerting any general influence over the 

 Venous circulation. The Pulmonary circulation being entirely within the 

 chest, cannot be affected by variations in atmospheric pressure; the entire 

 venous circulation of the foetus, also, is independent of any such agency. 

 Again, it has been shown experimentally by Dr. Arnott and others that no 

 suction power, exerted at the farther end' of a long tube, whose walls are so 

 deficient in firmness as are those of the Veins, can occasion any acceleration 

 in a current of fluid transmitted through it, for the effect of the suction is 

 destroyed at no great distance from the point at which it is applied, by the 

 flapping together of the sides of the vessels. This tendency may be counter- 

 acted, however, as Berard ' maintains, by firm adhesions of the external sur- 

 face of the Veins to the adjoining parts: such adhesions undoubtedly take 

 place in many parts, as for instance in the Hepatic and Innominate Veins, 

 and in the lower part of the Jugular Vein; and therefore, to that extent at 

 least, the venous circulation must be influenced by the respiratory move- 

 ments. 2 Another agency which certainly assists the venous circulation iu 

 some animals, is the rhythmical contraction of the walls of the Veins, which 

 has been observed to occur 8 to 10 times per minute in the transparent mem- 

 brane of the wing of the Bat, the amount of contraction being about one- 

 fourth of the diameter of the vessel (Wharton Jones). The same phenom- 

 enon repeated 5 or 6 times per minute has been observed by Schiff 3 and 

 Vulpian 4 in the veins of the Ear, and by Wagner 5 in the vessels of the Iris 

 of the Rabbit. It has also been shown by Mr. Wharton Jones 6 that the 

 Lymphatic Hearts of the Eel and Frog are to be regarded as exerting an 

 auxiliary agency on the general circulation, propelling their contents at cer- 

 tain intervals into the Veins. The walls of these hearts are composed of 

 unstriped rhythmically contractile muscular fibrils, which contract under 

 the influence of the spinal cord. 7 



275. One of the most powerful of the general causes which influence the 

 Venous circulation, is doubtless the frequently recurring pressure of the 

 muscles upon their trunks. When quiescent the circulation in muscles is 

 extremely slow, but whenever contraction takes place, a portion of the Veins 



1 Cours de Physiologic, t. iv, p. 62. 



2 The pressure of the blood in the veins has been carefully examined by MM. 

 Jacobson and Reoklinghausen (Yirchow's Archiv, Bd. xxxvi, p. 1), who found it to 

 be as follows in the sheep, when the animal was breathing naturally : 



Left vena innominata, . . . . 0.1 mm. of mercury. 



Kight sul-clavian vein, .... - O.I " 



Left snbclavian vein, .... - 0.6 " 



Right jugular vein, ....-)- 0.2 " 



Left jugular vein, ...... 0.1 



External facial vein, . . + 3.0 " 



Internal facial vein, . . -f- 5.2 



Brachial vein, +4.1 



Branch of the brachial vein, . . + 9-0 " " 



Crural vein, -j-11.4 about inch English. 



3 Archiv f. Physiol. Heilk , 1854, t. xiii, p. 521. 



4 Comptes Rendus de la Societe de Biologie, 1856, p. 183. 



5 Archiv f. Ophthalmol., Bd xii. Heft ii, p. 1. 



6 Proceed, of the Roy. Soc., 1868, Nos. 98, 101, and 102. 



7 See Eckhard, Beitrage, No. vii, p. 167. 



