"The name of Glisson occupies an honourable place in the history of medicine, because to him we are indebted for the first elements of the physiological doctrine of the present day. Instead of directing his attention to movements alone, as the iatro-mathematicians, and even, to a certain extent, the animists had done, he referred to vitality all the phenomena of nature, of whatever kind, and attempted to reduce them to one, common principle. To this end he admitted, that matter is originally endued with forces inherent in it, and that living bodies in particular, are invested in their organs with a radical force, which, put in play by stimulants, whether internal or external, gives rise to all the phenomena of life. He even went so far as to assert, that sympathy may be explained by referring to the intercommunication of this force, to which he gave the name of irritability."
We shall also cite from Sprengel, a passage which throws some light on his theory.
"When they became unwilling, like Descartes and Stahl, to have constant recourse in their explanations, to the soul, they tried to find a philosophic proof of the existence of material forces, to show that matter, as mere matter, is endowed with particular forces, with which they might satisfactorily explain a great many of its phenomena. No one had hitherto sought for a similar proof; for Aristotle had contented himself with an axiom, that all natural things contain in themselves the sufficient cause of their movement and rest. Glisson and Leibnitz set themselves in search of this proof; but it was reserved for the immortal Kant to find it in the nature of matter itself.
"Francis Glisson may with propriety be considered as the precursor of Leibnitz. What he tried to demonstrate by scholastic subtlety, and by thousands of syllogisms, was developed by Leibnitz with a clearness and ability, which secured the suffrages, even of the unenlightened. Both of them went too far, in attributing life and sensation to matter, instead of claiming for it the two simple and primordial forces of attraction and repulsion.
"Glisson sets out with the idea of substance, but he does not explain it with sufficient precision. Every substance has three substantial rudiments,—fundamental substance, by means of which it exists,—energetic substance, by means of which it acts,—and additional substance, which determines its accidental qualities. All matter, as substance, must have an energetic substance or nature, which is the internal principle of movement. Therefore whatever moves spontaneously, and in virtue of an internal force, must feel this motion, and desire it. All matter feels that it is, and that it exists by itself. It has therefore, consciousness of its own nature. Life consists in the activity of the internal substantial energetic nature. Death is the dissolution of the triple alliance of the internal energetic substantial nature, with the vegetative and animal natures, which two last belong to the additional substance."[28]
In applying his theory to physiology, Glisson's idea is, that the fibres of the human body are endowed with a force, which he divides into three kinds; to wit, natural or inherent force, (robur insitum)—vital force, (robur vitale)—and animal force, (robur animale.)
Natural or inherent force, is a part of the constitution of the fibre, and is as much a property of its organization as are its tenacity, tensibility, &c. The sum of this force varies, in proportion as the constitution of the fibre is more or less perfect. It is strongest in athletic men and strong animals, and weaker in relaxed and debilitated persons. It may be compared with the contractilité de tissu of Bichat.
The second, or vital force, is something superadded to the inherent sort. It is an influxus, derived to any fibre or set of fibres, from that greater sum of force, which arises out of a more elaborate, complex, and exalted organization. It varies in proportion as the vital spirits flow with more or less freedom; and in proportion as their quality is more or less perfect.
The third kind, or robur animale, may be supposed to depend on the organic constitution of the brain and nerves, and varies according to the state of that organization. We cannot help adverting to the resemblance between these two latter kinds, and the contractilité organique, and contractilité animale, of Bichat; and this robur comprises, as we shall show hereafter, both the contractilité and sensibilité of the French physiologist.
Glisson, in his chapter de Irritabilitate fibrarum, commences by remarking that a motive faculty existing in any fibre, unless it were of an irritable nature, would leave such fibre in one of the two following states: 1. It would either never cease from action, or 2ndly, being once at rest, its motion could never be reproduced; but the varieties and differences which we see in the actions of fibres, clearly demonstrate them to be possessed of irritability: i.e. if a fibre may be by turns in a state of action and repose, it is evidently possessed of a quality, whereby it can be induced to move if in a state of rest; this quality he terms irritable, or irritability. The next inference from this power of alternate activity and repose is, that the fibre is possessed of a faculty, whereby it can perceive an irritation offered to it; but this perception of irritation further implies an appetence for a change of its actual state, before the motion can really take place. Perception, appetence, and motion, make a triunit. "In the mean time, says he, as sensitive appetence, and sensibility, are frequently confounded with natural perception, in this irritation of the fibres," he divides it into three kinds, viz. Natural Perception, Sensitive Perception, and Perception regulated by animal appetency.