MODERN DEVELOPMENTS OF HARVEY's WORK/ 467 



is iiuiintiiiued was effected in tlie body. While keeping u}) the circulation 

 of blood through the vessels of muscles severed from the body, Ludwig- 

 and Sczelkow' observed variations in the flow which appeared to indi- 

 cate contractile power in the vessels themselves. This research was 

 carried on under Ludwig's direction by various of his scholars in suc- 

 cession, Alexander Schmidt, Dogiel, Sadler, myself, Ilafiz, Lcpine, A. 

 Mostio, \ on Frey, and Gaskell. Their observations, as well as those of 

 Cohuheim and Gunning, have shown that the muscular fibers of the 

 arterioles, not only in the muscles but throughout the body generally, 

 have a power of independent and sometimes rhythmical contraction 

 and relaxation. Their contractility is, however, controlled by the cen- 

 tral nervous system in accordance with the wants of the body generally, 

 i'or tlie amount of blood contained in tlie body is insufficient to fill the 

 whole of the vascular system at once, and when the vessels are fully 

 dilated, as they are after death, we find that nearly the whole of the 

 blood of the body may be contained in the veins alone. It is therefore 

 necessary that when one part of the body is receiving a larger supply 

 of blood another should be receiving a smaller supi)ly; and the func- 

 tions of the vaso motor centers have been well compared by Ludwig to 

 the turncocks in a great city, who cutoff' the water supply from one dis- 

 trict at the same time they turn it on to another. Thus it is that when 

 the brain is active the feet may get cold, and Mosso has shown this 

 ill an exceedingly neat manner by placing a man on a large board deli- 

 cately balanced at its center, and demonstrating that whenever the man 

 began to think the increased supply of blood to his brain caused the 

 head to go down and the heels to rise up. A similar condition was 

 indicated bj' Mayow, who gave a different explanation. lie said that 

 the vital spirits were not able to be in the same place at once, and there, 

 fore it happens that if a man eats a heavy meal he is apt to become 

 drowsy, because the vital spirits descend from the brain to the stomach 

 in order to carry on digestion; and, on the other hand, if a man thinks 

 vigorously after dinner the vital spirits have to leave the stomach to go 

 to the brain, and conse([uently digestion is imperfectly i)erformed. If 

 we substitute the word blood for vital spirits we have an exact expres- 

 sion of present j)hysiological ideas. 



Ubi stimulus ibi affluxus was an old doctrine and expressed a great 

 truth. Wherever the need for increased nourishment or increased sup- 

 ply of oxygen exists in the healthy body, thither does the blood flow in 

 larger quantities than usual. If the glands are active their blood snp- 

 l)ly is greatly increased, as was shown by Bernard, and a similar occur- 

 rence takes place in the contracting muscle, as has been shown by 

 Ludwig and his scholars. The vessels of the intestines and of the 

 skin, with their numerous glands, have their caliber regulated by the 

 vasomotor nerves which i)roceed from the center in the medulla oblon- 



' Ludwit;- and Sczolkow. Ileule and Pfeuffers Zeitschrift, 1863, Vol. XVll, page 

 1015 and vide page 122. 



