VASO-MOTOR NERVES. 739 



and this increase is greater with the induced than with the constant current. When the 

 sympathetic is divided, the quantity of urine and urea sinks to the minimum. 



Dr. Moreau has recently published a series of observations on the influence of the 

 sympathetic nerves upon the secretion of liquid by the intestinal canal, which are pecul- 

 iarly interesting in their bearing upon the sudden occurrence of watery diarrhoea. In 

 these experiments, the abdomen was opened in a fasting animal, and three loops of intes- 

 tine, each from four to eight inches long, were isolated by two ligatures. All of the 

 nerves passing to the middle loop were divided, taking care to avoid the blood-vessels. 

 The intestine was then replaced, and the wound in the abdomen was closed with sutures. 

 The next day the animal was killed. The two loops with the nerves intact were found 

 empty, as is normal in fasting animals, and the mucous membrane was dry; but the loop 

 with the nerves divided was found filled with a clear, alkaline liquid, colorless or slightly 

 opaline, which precipitated a few flocculi of organic matter on boiling. 



Vaso-Motor Nerves. * 



The experiments which we have already cited demonstrate beyond a doubt the exist- 

 ence of nerves distributed to the muscular coats of the blood-vessels and capable of. 

 regulating their caliber and the quantity of blood sent to different parts. These are the 

 vaso-motor nerves, discovered by Brown-Sequard, in 1852. The importance of nerves 

 apable of regulating what we may call the local circulations is sufficiently apparent. 

 The glands, for example, require at certain times an immense increase in their supply of 

 blood, and the same is probably true of the muscles, brain, and other parts. It has been 

 shown, by direct experiments upon living animals, that local variations in the circulation, 

 independent of the action of the heart, actually take place, and that they are of great 

 importance in special functions ; and there are numerous instances of such action, which 

 can only take place through the nervous system. The phenomena of blushing and pallor, 

 from mental emotions, are familiar examples. 



There can be no doubt of the fact that the sympathetic branches contain filaments 

 capable of modifying the caliber of the blood-vessels, and that the cerebro-spinal nerves 

 also contain elements possessing analogous properties ; but when we reflect upon the 

 extensive anastomoses, in both directions, between the sympathetic and the ordinary 

 motor and sensory nerves, we can appreciate the importance of determining the exact 

 origin and course of these vaso-motor fibres. The first important question is, whether the 

 vaso-motor filaments be derived from the sympathetic ganglia or from the cerebro-spinal 

 centres. 



All experiments upon the question just proposed tend to show that the vaso-motor 

 nerves are , derived exclusively from the cerebro-spinal system and do not originate in 

 the sympathetic ganglia. Without citing the numerous confirmatory observations of dif- 

 ferent physiologists, it is sufficient to state that Schiff has experimentally demonstrated, 

 in the most conclusive manner, that the vaso-motor nerves are derived from the cerebro- 

 spinal centres and not from the sympathetic ganglia. There is now no difference of 

 opinion among physiologists upon this point, the only question being the exact location 

 of the vaso-motor centres. 



As a summary of our present knowledge of the origin of the vaso-motor nerves in the 

 cerebro-spinal axis, we may cite the following remarks, from a review of the experiments 

 of Schiff, by Brown-Sequard : "1. That if there are vaso-motor elements which decus- 

 sate in the spinal cord, their number is excessively small. 2. That the facts observed by 

 M. Schiff, on this subject, admit of a more simple explanation. 3. That a number of the 

 vaso-motor elements stop in the spinal cord. 4. That a tolerably large number of vaso- 

 motor elements, coming from different points in the body, ascend as far as the tuber 

 annulare, and some as far as the cerebellum and to other parts of the encephalon. 5. 

 That, consequently, the medulla oblongata is not the sole source of the vaso-motor ele- 



