H 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



Gottingen lectures (63) gi\cn in 1752 (and published 

 the following year) that the concept is most full\- de- 

 veloped and supported by experimentation. Haller's 

 own definitions for the dual properties of irritability 

 and sensibility were as follows: "I call that part of the 

 human body irritable, which becomes shorter on 

 being touched; very irritable if it contracts upon 

 slight touch, and the contrary if by a violent touch it 

 contracts but little. I call that a sensible part of the 

 human body, which on being touched transmits the 

 impression of it to the soul; and in brutes, in whom the 

 existence of a soul is not so clear, I call those parts 

 sensible, the Irritation of which occasions evident 

 signs of pain and disquiet in the animal." 



One sees immediately the bogey of the early physi- 

 ologists raising its head — the necessity, on invoking 

 the soul, for differentiating processes in man from 

 those in animals. Haller describes his technique for 

 determining sensibility as follows: "I took living ani- 

 mals of different kind, and different ages, and after 

 laying bare that part which I wanted to examine, I 

 waited till the animal ceased to struggle or complain, 

 after which I irritated the part, by blowing, heat, 

 spirit of wine, the scalpel, lapis infinalis, oil of vine- 

 gar, and bitter antimony. I examined attentively, 

 whether upon touching, cutting, burning, or lacerat- 

 ing the part, the animal seemed disquieted, made a 

 noise, struggled, or pulled back the wounded limb, 

 if the part was convulsed, or if nothing of all this 

 happened." 



Haller recognized that nerves arc "the source of all 

 sensibility," but applied his dichotomy of irritability 

 and sensibility to various types of nerves, noting that 

 all nerves are not irritable according to his definition 

 (with its insistence on resultant contraction). He thus 

 approached the differentiation of motor and sensory 

 nerves. Still incorporated in his hypothesis was the 

 1600-year-old concept of a nervous fluid within the 

 nerves. It might be thought that once the microscope 

 had been invented, the question of whether or not 

 the nerves were hollow pipes might have been 

 quickly settled. Indeed in 1674 Leeuwenhoek (64), 

 with the limited magnification of his simple micro- 



63. VON Haller, A. De paitibus corporis humani scnsibilibus 

 et irritabilibus. Comment. Soc. reg. Set. Gottingen 2: 114, 

 1753; English translation by M. Tissot, M.D. A disserta- 

 tion on the sensible and irritable parts oj animals^ from a 

 treatise published in the Transactions of the Royal Society 

 of Gottingen and read in the .'\cademy of Gottingen by 

 Haller on April 22, 1752. Printed by J. Nourse at the 

 Lamb opposite Katherine-street in the Strand, 1755. 



64. VAN Leeuwenhoek, .■\ntonj (1632-1723). Phil. Trans. 9: 

 178, 1674. 



scope, had specifically searched for cavities in the 

 nerves of a cow but his results were equivocal. One 

 hundred years later this issue was still unresolved. 



The only competing hypothesis, which received 

 but little support, was that the nerves were cords 

 that communicated sensation to the brain by their 

 \ibrations (rejected by Boerhaave as "repugnant to 

 the Nature of the soft, pulpy and flaccid nerves"). 

 This view was also rejected by Haller. 



In considering how a fluid could possibly flow as 

 swiftly as nerves can be observed to act, Haller pro- 

 posed that it must indeed be a very subtle fluid imper- 

 ceptible to the eye yet more substantial than heat, 

 aether, electricity or magnetism. In another comment 

 he granted that electricity was a most powerful stimu- 

 lus to nerves but that he thought it improbable that 

 the natural stimulus was electrical. Thinking always 

 in terms of electricity flowing as down a wire, Haller, 

 like so many physiologists after him, felt the lack of 

 insulation around the nerve to be a critical argument 

 against nervous influence being electrical. 



However, the notion of electricity as a transmitter 

 of nervous acti\ity kept cropping up at about this 

 time. Alexander Monro (65), Professor of Medicine 

 and Anatomy in the University of Edinburgh, a 

 pupil of Boerhaave and first of the great dynasty of 

 Monros, pointed out that no cavities could be seen in 

 nerves, that no drops of fluid came out when a nerve 

 was cut, and that the nerve did not swell when ligated; 

 and he rather cautiously skirted the possibility of 

 electricity being the agent. But he too considered it 

 only in terms of electricity running down a wire and, 

 like Haller, was bothered that the nerve was inade- 

 quately insulated to prevent loss. "We are not suffi- 

 ciently acquainted," he said, "with the properties of 

 aether or electrical effluvia pervading everything, to 

 apply them justly in the aniitial oeconomy; and it is 

 difficult to conceive how they should be retained or 

 conducted in a long nervous cord." 



Electricity had also been suggested by Stephen 

 Hales (66) in refuting a suggestion that the swelling 

 of muscles was due to inflow of blood. This country 

 clergyman, without formal scientific or medical train- 

 ing, by his experimental skill and keen observation 

 became one of the outstanding contributors to knowl- 

 edge of the circulation. In writing of the nerves he 

 said, "From this very small Force of the arterial Blood 



65. Monro, .-Xlexander (1697-1762). The works of Alexander 

 Monro (collected by his son). Edinburgh: Charles Eliot, 

 1781. 



66. Hales, Stephen (1677-1761). Statical Essays. London: 

 Innys and Manby, vol. I, 1726; vol. II, 1732. 



