490 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



stricter centre is bilateral, lying in the anterior part of the lateral columns on 

 both sides of the median line. 1 At this site is found a group of ganglion-cells 

 known as the antero-lateral nucleus of Clarke. It is possible, though far 

 from certain, that these are the cells of the vaso-constrictor centre. 



The vaso-constrictor centre in the bulb is always in a state of action, or 

 " tonic " excitation, as is shown by the dilatation of the vessels when deprived 

 of their constrictor impulses through the section of the spinal cord. 



It is not definitely known whether a vaso-dilator centre is present in the 

 bulb. 



Spinal Centres. A complete demonstration of the existence of vaso-motor 

 centres in the spinal cord, first suggested by Marshall Hall, was made by Goltz 

 and Freusberg 2 in their experiments on dogs which had been kept alive after 

 the division of the spinal cord at the junction of the dorsal and the lumbar 

 regions. This operation cuts off both sensory and motor communication 

 between the parts lying above and below the plane of section, and divides the 

 animal physiologically into a fore dog and a hind dog, to use the author's 

 expression. The investigator can now explore the lumbar cord unvexed by 

 cerebral impulses. A great number of motor reflexes formerly thought to have 

 their centres exclusively in the brain are by this means found to take place 

 in the absence of the brain. 3 That vaso-motor reflexes were among them was 

 discovered by accident. It was noticed that the mechanical stimulation of the 

 skin of the abdomen and penis while the animal was being washed provoked 

 erection, which, as Eckhard 4 had discovered some years before, is a reflex action 

 due to the dilatation of the arteries of the penis through impulses conveyed by 

 the nervi erigentes. Pressure on the bladder, or the walls of the rectum, also 

 had this effect. After the destruction of the lumbar cord this reflex was no 

 longer possible. The vessels of the hind limb are also connected with vaso- 

 motor cells in the lumbar cord. Soon after the section of the cord in the dorsal 

 region the hind paws are observed to be warmer than the fore paws, and the 

 arteries of the hind limb are seen to beat more strongly. This is the result of 

 cutting off the vaso-constrictor impulses from the bulbar centre to the vessels 

 in question. If the animal survives a considerable time the hind paws will 

 be observed to grow cooler from day to day until they are again no warmer 

 than the fore paws. Destruction of the lumbar cord now causes the tempera- 

 ture of the hind limbs to rise again. 



The conclusion drawn from these observations is that vaso-motor cells are 

 present in the spinal cord. It is probable that they are normally subordinated 

 to the bulbar nerve-cells and require a certain time after separation from the 

 bulb in order to develop their previously rudimentary powers. Hence the 



1 Dittmar, 1873, pp. 110, 114. Other literature : Schiff, 1855, p. 198 ; Heidenhain, 1870, 

 510; Latschenberger and Deahna, 1876, p. 183; Strieker, 1886, p. 13. 



2 Goltz and Freusberg, 1874, p. 463. Other literature: Smirnow, 1886, p. 145; Ustimo- 

 witsch, 1887, p. 187 ; Thayer and Pal, 1888*, p. 29 ; Konow and Stenbeck, 1889, p. 409. 



3 Later experiments by Goltz and Ewald, showing the degree of independence of the spinal 

 cord possessed by sympathetic vaso-motor neurons will presently be cited. 



* Eckhard, 1863, p. 144. 



