SECT. III.] PROPERTIES OF THE VIS NERVOSA. 395 



but when tlie bones are softened by some morbific cause, the 

 constriction of the foramina is relaxed, and the nerves no longer 

 strangulated again become sensitive. That bones morbidly 

 softened are rendered sensitive, is proved by the observations 

 of Deidier and Petit. He also found that the slightest touch 

 of a carious bone excited intense pain.^ Murray rightly ob- 

 serves, that the following questions are worthy the diligent 

 investigation of physiologists : — how does it happen that nerves 

 entering the substance of bones, are compressed and strangu- 

 lated in the narrow foramina for many years, and thus ren- 

 dered unfit to excite sensation, yet when the bone is softened 

 and the constriction of the nerves diminished, they again become 

 fit for sensation, nay, acquire the most exquisite sensibility ? 

 If the nerves be small channels for a nervous fluid, they are 

 compressed so long that the channels ought to coalesce, and the 

 nerves be impermeable ever after to the nervous fluid. Then this 

 author seems to ask, why is it that in disease of the bones we 

 often find so much more sensibility than could be expected from 

 so few and such minute nerves ? The increased sensibility, or 

 vis nervosa, seems to compensate for this paucity of the nerves. 

 V. When the vis nervosa is diminished. — The vis nervosa 

 is diminished in proportion as we observe the vital powers 

 which are dependent on the vis nervosa, to be diminished and 

 weakened; and which becomes so weak in death, that the natural 

 stimuli, as for example, the influence of the inspired air, and of 

 the blood in the heart, can no longer excite it, and a mortal 

 repose of all the vital and animal movements results. In this 

 ordinary termination of life, the vis nervosa is undoubtedly at 

 a minimum, but it is not quite lost, for a few sparks can still 

 be excited, if a strong stimulus be applied to the nerves. 

 Vesalius was taught this fact by sorrowful experience, for when 

 dissecting a body shortly after death, he excited the heart to 

 renewed action. Brunner^ succeeded in doing the same thing 

 in the bodies of men and various animals, by forcing air into 

 the heart, through the thoracic duct or veins. In many expe- 

 riments on frogs, I observed, that when the heart was still and 



* Brambilla, Surgeon in Ordinary to the Emperor Joseph II, and First Surgeon to the 

 Guards, &c., also demonstrated the sensibility of diseased bones before the author at 

 Vienna. 



* Parerg. Anat. Genevae, 1681. Miraculum anatomicum in cordibus resusci- 

 tatis, &c. 



