178 ACTION OF NITRITE OF AMYL ON THE CIRCULATION, ETC. 



the vaso-motor uerves derive from the medulla oblongata, another 

 series of experiments was undertaken. This question was the 

 more interesting from its connection with another research 

 which I began under Professor Ludwig's direction, but unfortu- 

 nately have not yet finished. Professor Ludwig observed, and 

 directed my attention to the fact, that the alterations in the 

 lumen of arteries noticed by Schiff in the rabbit's ear, may be 

 seen also in all exposed arterial twigs in the skin and connective 

 tissue They vary in amount and rapidity in different animals, 

 and in the same animal at different times. They are sometimes 

 absent, but in such cases may be generally produced by poison- 

 ing with curare, or by suspending the respiration ; and when 

 once aroused, they continue some time, although the respiration 

 be afterwards most carefully performed. 



That these alterations are, at least in part, completely inde- 

 pendent of the vaso-motor nerves in the brain is shown by their 

 occurrence in the ear and other parts, after all the nerves, 

 sympathetic and cerebrospinal, going to tlie part have been 

 divided, and after division of the cord in the neck notwithstand- 

 ing the low pressure which then remains. 



The form of the variation shows that they do not depend on 

 varying blood-pressure in the large arteries ; for sometimes a 

 contraction suddenly appears between two parts of the artery 

 filled with blood, and in one case in the rabbit's ear I noticed 

 such a contraction take place in a small artery at the point 

 where it branched off from a larger one, and proceed peristaltically 

 downwards. 



The lightest touch on an artery after division of the nerves 

 causes a movement generally limited to the part, and consisting 

 not in a contraction, but in dilatation, w^hich remains for some 

 time, and gradually disappears. As Gunning and Cohnheim 

 have made similar observations on the tongue and web of the 

 frog, and some facts in Sadler's research {Ludivig's Arheiten, 

 4ter Jahrg.) can only be explained by an independent motion of 

 the vascular walls, it seems to be a widely extended and there- 

 fore important phenomenon. If the nitrite acts through the 

 vaso-motor centres in the brain, it should have no eiffect if these 

 be separated from the vessels by dividing the cord in the neck, 



