x VASCULAR MUSCLE AND NERVES 363 



to the circulation. After destruction of the central nervous 

 system, there is a marked dilatation of the visceral vessels, 

 particularly of the veins, in consequence of which nearly the 

 whole of the blood collects in those vessels, while the remaining 

 parts of the body are much impoverished. On exposing the 

 beating heart, he saw that it was almost bloodless, since very little 

 blood reached it during diastole, and therefore very little could be 

 expelled into the aorta during systole. It follows that vascular 

 tonicity is an indispensable condition of the circulation, and that 

 not merely the arteries, but the veins as well, possess a tone that is 

 dependent on the central nervous system in general. 



The bulbar centre for the vaso-constrictors was more exactly 

 localised and determined in the subsequent investigations of 

 Owsjannikow (1871) and Dittmar (1873), in Ludwig's laboratory. 

 Starting from the fact that central excitation of the sciatic in 

 curarised dogs and rabbits, even after separation of spinal bulb 

 from brain by a transverse section, reflexly produces a perceptible 

 increase in arterial blood-pressure, they endeavoured to define the 

 region of the bulb in which this reflex occurred. With this 

 object Owsjannikow made successive cross-sections from above 

 downwards at different heights of the medulla, and examined both 

 the depressor effect of each section, and the reflex pressor effect on 

 exciting the sciatic. The upper limit of the vascular centre lies 

 at the level of that section after which there is a fall in aortic 

 pressure, and a diminution in the height of the reflex rise of 

 pressure; the lower limit is at that section after which aortic 

 pressure reaches its minimum, and no longer rises on excitation 

 of the sciatic. By pursuing this method, with the guidance of 

 the above data, he decided that the bulbar vasomotor centre in 

 the rabbit is about 4 mm. high ; its upper limit is 1-2 mm. below 

 the corpora quadrigemina, its lower limit 4 mm. above the point 

 of the calamus scriptorius. Since longitudinal section of the bulb 

 in the median line produces no perceptible fall in aortic pressure, 

 he concludes that the centre is not in the median line, but consists 

 of two centres situated at either side of the bulb. 



Dittmar, who practically confirmed the results of Owsjannikow 

 in regard to the longitudinal extension of the bulbar vascular 

 centre, went on to establish its limits in the two other dimensions, 

 by the same method of systematic sections. He discovered that in 

 each half of the bulb there is a small prismatic space, on destroying 

 which the reflex vascular constriction is abolished. In this area 

 a nucleus of grey matter is visible under the microscope, described 

 by Clarke as the antero-lateral nucleus, in the rabbit. 



The main results of Ludwig's pupils were subsequently con- 

 firmed by Heidenhain, Berkowitsch, Latschenberger, and Deahna. 



VII. After Ludwig's School had investigated the bulbar vaso- 

 constrictor centres, and had shown that after destroying their 



