680 



CIRCULATION. 



the heart alone. We shall only remark in 

 this place that although the heart may be 

 excited to contraction by the direct stimu- 

 lation of its muscular substance, and although 

 the effect upon the heart's action of bodily 

 exertion, of emotions of the mind, and of 

 severe injuries of the brain and spinal mar- 

 row, all of which can be supposed to act upon 

 the heart through the nerves only, are un- 

 doubted ; yet it is well' ascertained that the 

 heart cannot in general be excited to con- 

 traction by the direct stimulation of its nerves, 

 and that its action may be regarded as auto- 

 matic to a certain degree, and little dependent 

 upon the immediate transmission to it of any 

 nervous influence from the cerebro-spinal or 

 ganglionic nervous systems, since the rythmic 

 contraction of the heart continues to go on for 

 a time in some animals after the division of its 

 nerves, and in others even after its complete 

 separation from the body. It has also been 

 frequently found that after the complete de- 

 struction of the brain and spinal marrow of an 

 animal the circulation of the blood can be 

 maintained for some time by means of artificial 

 respiration, an experiment which proves that 

 the motion of the blood in the vessels is not 

 immediately dependent upon nervous influ- 

 ence.* 



Many circumstances, however, seem to shew 

 that the state of the vessels, and in consequence 

 of this the velocity and force of the blood, are 

 susceptible of very considerable modification 

 from local affections of the nerves belonging to 

 the part in which they may have been observed 

 to occur, or from general alterations of the 

 nervous powers of the system. It is probable 

 that nervous influence operates much more 

 powerfully in modifying the circulation through 

 the small than through the large vessels, indeed 

 we know of no direct satisfactory experiments 

 which demonstrate the effect of nervous in- 

 fluence upon the larger arteries exclusively. 



The experiments which seem to prove most 

 satisfactorily the influence of the nervous system 

 on the circulation in the small vessels are those 

 performed on cold-blooded animals by Legal- 

 lois,f W. Philip, J Flourens, and particularly 

 those of Marshall Hall, the general result of 

 which may be stated as the following : that after 

 the destruction, whether sudden or gradual, of 

 the brain or spinal marrow, the flow of blood 

 in the remote parts becomes more languid 

 and is gradually more and more circumscribed, 

 while the action of the heart continues, and its 

 power seems not to be diminished in a propor- 

 tional degree. But in such experiments as those 

 just mentioned, performed in general in cold- 

 blooded animals, it must be at all times ex- 

 ceedingly difficult to find an accurate mode of 

 measuring the force of the heart, and conse- 



* We refer here to the experiments of Haller, 

 Whytt, Fontana, Spallanzani, Legallois, W. Philip, 

 Cli.t, Flourens, and Miiller ; Humboldt, Fowler, 

 Brachet, Treviranus, Weinhold, &c. 



f Exper. sur le Principe de la Vie. 



j Exper. Inquiry into the Laws of the Vital Func- 

 tions. 



Loc. citat. p. 99. 



quently they cannot be regarded as affording 

 sufficient evidence that there did not occur 

 along with the languid state of the circulation 

 a certain diminution in the heart's power. 

 They do not at least entitle us to conclude that 

 the decreased velocity and stagnation of the 

 blood in the remote parts is caused mainly by 

 the loss of the vital powers of the capillary 

 vessels, for these changes of the circulation 

 may in a great measure be the effect of other 

 causes, as the loss of power of the heart, and 

 that more permanent alteration of the textures 

 which very probably accompany the severe 

 injury done to the body. On the other hand 

 it may be remarked that the coldness and im- 

 paired nourishment common in palsied limbs, 

 the known increase or diminution of the various 

 secretions from mental emotions, and direct 

 or sympathetic affections of the nerves belong- 

 ing to the glands or other secreting organs, 

 the phenomena of blushing, erection, inflam- 

 mation, and the like are all very direct and 

 satisfactory proofs that the small vessels and 

 the capillary circulation may be influenced by 

 affections of the nerves. As a further confirma- 

 tion of this may be mentioned, 1, the inflamma- 

 tion and other consequences of the division of 

 the fifth pair of nerves which occur in the eye; 

 2, the statement of some, as Treviranus, that 

 the division of the nerves of the leg of a frog 

 impedes the circulation: 3, the assertion by 

 others, as Baurngartner, that after the division 

 of the nerves or the destruction of the spinal 

 marrow, the peculiar oscillations which he, 

 along with Doellinger and Kaltenbrunner, has 

 observed to precede the formation of new blood- 

 vessels do not occur ; and 4, the observations 

 of Nasse, which are stated to shew that the 

 reunion of wounds is retarded or put a stop to 

 by the division of the nerves belonging to the 

 wounded part. Krimer,* whose experiments 

 on this subject are numerous and remark- 

 able, states that the circulation was always much 

 impaired by the abstraction of nervous influ- 

 ence from the division or ligature of the nerves; 

 that the jet from the femoral artery of a qua- 

 druped was much less strong after the division 

 of the crural nerve ; that the capillary circula- 

 tion of the frog's web ceased soon after the 

 nerves were cut or tied ; that the arterial blood 

 passed through the systemic capillaries without 

 undergoing its proper change into venous ; 

 and that salt did not produce the accustomed 

 effect of dilating the capillaries when the nerves 

 of the part were injured, but that these effects 

 were induced when galvanic irritation was 

 applied to the divided nerve. 



In reference to these experiments it may be 

 remarked that most of them are at variance 

 with experiments of a similar nature performed 

 by others, more especially those of Haller, 

 Spallanzani, Whytt, Fontana, Legallois, W. 

 Philip, Flourens, and M. Hall, none of whom 

 remarked so immediate and complete a stoppage 

 of the circulation from removal of the nervous 

 influence. Again, in palsied limbs the circu- 

 lation is frequently little or not at all disturbed, 



* Physiologische Untersuchungen. Leipzig, 1820. 



