General Physiology: An Outline of the Science of Life

In this circumstance lies Haller's great importance in the development of physiology. The grouping of a heterogeneousmass of facts into a closed and intelligible whole is always stimulating and fruitful, and this explains the immense authority and powerful influence which Haller exercised in the development of physiological investigation. His own physiological researches, however, while very conscientious and exact, as, e.g., those upon the respiratory movements and the theory of irritability, contain no epoch-making discoveries, and some of them even had the misfortune to play an obstructive role in the further development of the science. This is especially true of two doctrines which he advocated — the so-called theory of preformation, and the theory of irritability.

The theory of preformation (theory of incasement) arose in connection with the microscopic observations upon the development of the ovum which were made in the seventeenth century. When it was seen how from a single small egg a complete animal was developed by the gradual maturing of one organ after another, the idea arose that all organs appearing in the course of development and, in brief, the whole animal, are preformed or already enclosed as such within the egg, and are made visible to the eye only by a process of growth and unfolding ; that, therefore, the human egg or, as some believed, the spermatozoon, is a minute but a completely formed homunculus. The necessary consequence of this idea was the assumption that at the creation of the world all coming generations were contained, already preformed, in the egg of each animal. The preposterousness of this view led a young physician, Caspar Friedrich Wolff (1733-1794) to maintain a new theory in opposition to that of preformation. Wolff's " theoria generationis" which later became the basis of all our modern ideas of the development of organisms, denied incasement and put in its place epigenesis. This asserted that all organs of the body are formed one after another in the course of development, in other words, that they originate as entirely new parts and have never pre-existed as such in the egg. Haller could not accept the idea of epigenesis, but opposed it energetically ; and, supporting the dogma of preformation with his whole authority, he retarded progress in the doctrine of animal development for more than half a century.

Haller's theory of irritability influenced the development of physiology in a somewhat different manner. Haller's own researches in this direction were experimental and very exact, and materially advanced the general theory of irritability ; but they were misinterpreted in various respects and extended by his followers, and formed the chief starting-point of a doctrine that confused all physiology down to the middle of the present century, and even now emerges again here and there in varied form. This is the doctrine of vital force. The fact of the irritability, or the direct excitability, of muscles had been emphasized by the earlier iatrophysicists, especially by Glisson (1597-1677). Haller took up the

question, and added the experimental proof of the fact that the muscle-fibre possesses the property of contracting upon stimulation independently of nervous influence, a quality which he sharply distinguished as irritability from the sensibility belonging to nerves. This sharp distinction affirmed a difference between the excitation of nerve and that of muscle which did not correspond wholly to reality, and awoke in many of Haller's adherents and followers the need of demonstrating irritability to be a uniform phenomenon.

This was attempted most successfully by an Englishman, John Brown (1735-1788), a gifted but careless thinker. Brown recognised in general a single excitability common to the nervous and muscular system, which system he regarded as a unit. The capacity of becoming excited by stimuli is possessed by all living nature, and is, indeed, the fundamental characteristic by which living beings, animals and plants, are distinguished from lifeless. Regarding the nature of excitability, Brown, like all other physiologists of the time, had little to say.

The hopes of the iatromechanics and iatrochemists of being able completely to resolve vital phenomena into physics and chemistry were not fulfilled. In irritability there existed a phenomenon which, as was believed, distinguished all organisms from lifeless bodies, and appeared to mock at a physico-chemical explanation. The unexplained conception of irritability, therefore, in union with the dynamical systems of Hoffmann and Stahl still prevailing, became the starting-point of vitalism or the doctrine of vital force, which in its most complete form asserted a distinct dualism of living and lifeless nature. This tneory appeared first in France, especially in the School of Montpellier, and later in Germany, and its hazy notions of vital force soon controlled all physiology. In France vitalism was founded by Bordeu (1722-1766), developed further by Barthez (1734-1806) and Chaussier (1746-1828), and formulated most distinctly by Louis Dumas (1765-1813). The vitalists soon laid aside more or less completely mechanical and chemical explanations of vital phenomena, and introduced, as an explanatory principle, an all-controlling, unknown and inscrutable "force hyper me'chanique." While chemical and physical forces are responsible for all phenomena in lifeless bodies, in living organisms this special force induces and rules all vital actions. In Germany vitalism did riot reach this degree of clearness. Its founder, Reil (1759-1813), differed from the French vitalists, and in his treatise " Ueber die Lebenskraft " expressed fairly clearly the view that the phenomena of living organisms are chemico-physical in nature, but that principles are at the same time in control which are conditioned exclusively in organisms by the characteristic form and composition of living substance.

Later vitalists, however, attempted no analysis of vital force ; they employed it in a wholly mystical form as a convenient explanation of all sorts of vital phenomena, and they distinguished several varieties. The " nisus formatiwis" e.g., or peculiar " formative effort," offered a simple explanation of the forms of organisms, accounting for the facts that from the egg of a fowl a fowl and no other species always developed, and that the offspring of dogs are always dogs. In place of a real explanation a simple phrase, such as " formative effort," or " vital force," was satisfactory, and signified a mystical force belonging to organisms only. Thus it was easy to " explain "the most complex vital phenomena.

But some investigators were not content with this kind of explanation, and, while indifferent to the doctrine of vital force, continued to search for a chemico-physical explanation of vital phenomena. They received a strong stimulus from the new discoveries of Galvani (1737-1798), who proved that electricity is produced by the living animal body, especially by the nerves. Naturally the value of this fact was very soon overestimated, and under the ban of the prevalent philosophy of nature, particularly as a result of the researches of Ritter (1776-1810) and partly also those of Alexander von Humboldt (1769-1859) and others, who extended Galvani's experiments, the idea arose and later became very popular, that the galvanic current is the cause of all vital phenomena, and even that all phenomena of all nature may be explained in general by galvanic polarity.

The great chemical discoveries of the previous century also influenced the development of physiology. Vegetable physiology was especially advanced by Ingenhouss (1730-1799), who developed the theory of the consumption of carbonic acid by plants. The discovery of oxygen by Priestley (1733-1804) and Lavoisier (1743- 1794), which was so momentous for physiology, bore its first fruits when Girtanner (1760-1800) showed that venous blood receives oxygen in the lungs from the inspired air. Thus the old doctrine of the pneumu, which controlled physiological ideas for centuries, was justified in modern form, and at the same time the ingenious idea of Mayow, who had compared respiration to a process of combustion, was raised to the rank of a fundamental physiological fact.

Besides the physical and chemical discoveries of that time, those in anatomy led also to important physiological results. Most prominent among these was the fundamental law of special nervephysiology, announced by Charles Bell (1774-1842), and later proved experimentally by Johannes Miiller, which affirms that the posterior roots of the spinal nerves are sensory (conducting centripetally), while the anterior roots are motor (conducting centrifugally).

Finally, in microscopy Spallanzani (1729-1799), and later especially Treviranus, obtained the distinction of having disproved experimentally by careful researches the theory of the spontaneous generation of animalcules in putrid infusions ; they snowed that these lowest of all living things develop only from germs which are to be found everywhere in the air and the water, and that even here Harvey's dictum " omne vivum ex ovo " admits of no exception.

England and France produced the most of these exact researches, while in Germany the most prominent thinkers, such as Oken, were swept on by the philosophy of nature with its powerful tendency toward pure speculation in the fields of natural science. Johannes Miiller 1 (1801-1858) is one of those monumental figures that the history of every science brings forth but once. They change the whole aspect of the field in which they work, and all later growth is influenced by their labours.

Like the other investigators of his time Miiller was a vitalist, but his vitalism had an acceptable form. To him vital force was something different from the forces of lifeless nature, but its administration rigorously followed physico-chemical laws, so that his whole endeavour was to explain vital phenomena mechanically. In doing this he went over the whole field of vital activities uniformly, neglecting no part, and by his own investigations, which were always original, he laid the foundations upon which we work to-day. He always kept his attention directed towards the whole ; he never undertook special investigations which would not help him to solve some large general problem. His ingenuity — and it is this that is so much missed in the more recent physiology — was expressed in the manner in which he attacked problems. He did not recognise one physiological method alone, but employed boldly every mode of treatment that the problem of the moment demanded. Physical, chemical, anatomical, zoological, microscopic and embryological knowledge and methods equally were at his disposal, and he employed all of these whenever it was necessary for the accomplishment of his purpose at the time.

The philosophy of nature experienced its most luxuriant growth during this time under the influence of the ideas of Schelling and Hegel, and with its unbridled speculation, which lacked all basis of fact, seriously threatened scientific investigation. But it exercised only the most beneficent effect upon the rigorously critical mind of Miiller. He recognised in the ambitious tendencies of the natural philosophers a germ of truth, and under its influence fashioned his own manner of scientific investigation into a genuinely philosophical type. While keeping constantly in view the large

1 The most important estimate of Johannes Miiller is to be found in the memorial address upon him given by du Bois-Reymond ('59). problems and the goal of science, he regarded critically the special methods and questions only as means to an end, as means for arriving at a harmonious comprehension of nature. Throughout his whole life he remained steadily true to this philosophical conception of science, which he had set forth with energy in his inaugural address, " Von dem Bedurfniss der Physiologie nach einer philoso- p'kischen Naturbetrachtung" It is remarkable that, notwithstanding the unalloyed admiration aroused by the figure of Mtiller, the later physiology has often wholly neglected this element. This is particularly noticeable in two fields in which from his youth up he took the most active interest, — that of psychology, and that of comparative physiology.

Psychology is avoided by the physiology of to-day almost with fear, an attitude that is in peculiar contrast with that of Mtiller. He regarded physiology as essential to advance in psychology by empirical methods, and in his examination for the doctorate he defended the thesis, " Psychologies nemo nisi physiologus" Un- doubtedly, the science of psychology ought not to be considered as simply a part of physiology. But the achievements of physiology in the field of the nervous system and the sense-organs are of so fundamental significance for psychology, that it may be said that the former science is more nearly related than any other to the latter. Mtiller 's own labours show very clearly with what success physiology is capable of handling psychological problems, for scarcely any physiological discovery has a more important bearing upon all psychology and the theory of knowledge — although unfortunately it is not generally appreciated — than the doctrine of the specific energy of the nerves or organs of the special senses. This doctrine affirms that different stimuli of whatever kind, when applied to the same sense-organ, e.g. the eye, are capable of calling forth only one and the same kind of sensation, namely, that sensation that is mediated by the sense-organ in question under the influence of its natural stimulus, in the case of the eye, light. Vice versa, one and the same stimulus, when applied to different senseorgans, calls forth entirely different sensations according to the nature of the organ upon which it works. This doctrine is founded upon two fundamental facts: first, that in reality the external world is not what it appears to us to be when perceived through the spectacles of our sense-organs ; and, second, that by the path of our sense-organs we cannot arrive at an adequate knowledge of the world.

Besides this fundamental proposition, however, Mtiller discovered many other important psychological facts, which he has presented in his works ; " Zur vergleichenden Physiologie des Gesichtssinnes des Menschen und der Thiere," " Ueber die phantastischen Gesichtserscheinungen" and the section " Vom Seelenleben " in his " Handbuch der Physiologie des Menschen!' Miiller's teacher Rudolphi had said : " Comparative anatomy is the surest support of physiology ; without it physiology is scarcely conceivable." Miiller was incited by this idea, and the result was the foundation of a wholly new science in his comparative physiology. Throughout his whole life he defended the position expressed in the words, " Physiology can be only comparative," and among the very large number of his physiological works there are few in which the comparative principle is not more or less clearly expressed.

He presented the results of his own investigations together with practically all the physiological knowledge of his time in his " Handbuch der Physiologic des Menschen" This work stands today unsurpassed in the genuinely philosophical manner with which the material, swollen to vast proportions by innumerable special researches, was for the first time sifted and elaborated into a unitary picture of the mechanism within the living organism. In this respect the " Handbuch " is to-day not only unsurpassed, but unequalled. Naturally many of its details are incorrect according to present ideas ; later researches performed with a more perfect technique have greatly extended and transformed some departments ; even many of Miiller 's general physiological ideas, such as that of vital force, have been completely abandoned by the later physiology ; nevertheless, it remains that of all the numerous handbooks that have since appeared none has reached that of the great master as regards the mode of dealing with the material. Most of the later Hand-books, Text-books, Elements, etc., although intended almost exclusively for the use of students, do not take the trouble to point out even briefly the aims, the problem and the purpose of physiological science, let alone giving to the matter as a whole a philosophical treatment in Mtiller's sense. Such a lack must be regarded as a serious detriment by thinking students who do not learn simply by rote. Only a very few text-books form an exception to this, as, e.g., Briicke's admirable " Vorlesungen uber Physiologic."

The tireless physiological activity of Mtiller, which won for him the fame of being the greatest physiologist of all time, did not prevent him from giving himself up in the later years of his life with equal enthusiasm to morphology, especially zoology, comparative anatomy, and paleontology, and of acquiring the name of the greatest morphologist of his time. So many-sided and comprehensive was he that by his own fundamental labours he mastered two large sciences, either one of which a single person is at present hardly able to survey unaided.

It is no wonder that so large a realm could not be held together as a unit after the death of its ruler. Like Alexander's universal empire, it became divided into many small territories, each one of which controlled itself; and with the present boundary of science it would be difficult to find a worthy successor to Miiller, even if he were endowed with the latter's superhuman power of labour. Morphology had become independent long before Mtiller. Soon after his death the course of physiology became divided and directed along purely chemical and purely physical paths.

Movement in the chemical direction was guided by Wohler (1800-1882) and Liebig (1803-1873). In the year 1828 Wohler gave the theory of vital force its death-wound by his epoch-making synthesis,out of purely inorganic substances,of urea, a body produced in nature only by organisms. It had been believed that substances that were produced by the organism were produced only through the activity of vital force ; but here for the first time a very characteristic material product of the animal body was manufactured artificially in the chemical laboratory. This synthesis was soon followed by others. Justus von Liebig established new views regarding the metabolism of organisms ; and later Voit, Pfltiger, Zuntz, and others, advanced the theory of metabolism further, though not in entire agreement with one another. Physiological chemistry became more and more independent, partly under the influence of Mulder and Lehmann, who first made a survey of the field, and especially under that of Kuhiie, who by his original methods and investigations, particularly upon the chemico-physiological relations of the proteids, diffused new light and expressed his conception of the science in his text-book. Finally, most recently, through the labours of Hoppe-Seyler, Hammersten, Bunge, Halliburton, Baumann, Kossel, and others, physiological chemistry as an independent science has quite cut itself loose from physiology, to the detriment of the latter.

E. H. Weber (1795-1878), Volkmann (1801-1877), Ludwig (1816-1895), Helmholtz (1821-1894), du Bois-Reymond (1818- 1896), Marey, and others, led the movement in the physical direction. Ludwig mechanically transmitted the rhythmic changes of pressure of the pulse to a moving writing-lever, and made them record themselves upon the smooth surface of paper moved at a uniform rate (Fig. 1). He thus surpassed all others in creating a method of the greatest value in the investigation of the purely physical activities of the animal body. This graphic method proved so extremely fruitful that it found wide employment in physiology. It was used for the graphic representation of muscle-contraction, of respiratory movements, of the heart-beat, etc. In France, Marey developed it to unexpected completeness ; so that now it serves as the most important method of investigation in all researches that deal with the phenomena of macroscopic movement. One other method became fundamentally important in physical physiology, namely, that of the comprehensive and ingenious technique of galvanic stimulation, which was created by E. du Bois-Reymond's classic researches upon the general physics of muscle and nerve.

By the perfection of this technique du Bois-Reymond made the galvanic current of all stimuli the most convenient to employ and FIG. 1. — /. Lud wig's kymograph. One limb of the manometer is connected with an artery at A ; the blood-pressure is transmitted to the column of mercury (represented in black), thence to the float upon the mercury in the other limb, and puts this float with its writing-lever in motion. The writing-lever inscribes its movements upon the drum, C, which is kept in constant rotation by a clock-work, B. (From BrUcke). 11. Pulse-curve from a rabbit. The small waves represent the variations in blood-pressure that constitute the pulse ; the large waves, the variations that the blood-pressure undergoes as the result of respiration.

the most capable of fine gradation and easy localisation for nerves and muscles; for these reasons it now holds the first place stimulation-experiments. The wide applicability of this ingenious physical method is due to the perfection of the technique of vivisection on the part of the great French physiologists, Magendie (1783-1855) and Claude Bernard (1813-1878). Claude Bernard guided operative physiology to its highest development, without at the same time becoming narrow. He was a philosophical investigator who in his researches kept in view the general problems of life. It is no wonder, therefore, that all French physiology of to-day must be considered as of Claude Bernard's school.

In comparison with the chemical and physical features of physiology, after Johannes Mliller's death other features receded into the background, or were entirely neglected. Psychological research was advanced especially by discoveries regarding the physiology of the sense-organs, in which the ingenious investigations of Helmhoi tz and Hering led to most important results, and the physiology of the central nervous system of higher vertebrates, knowledge of which was perfected by the epoch-making labours of Flourens (1794-1864), Hitzig, Munk, Goltz, Horsley, and others. Preyer's endeavour to follow the development of the psychical phenomena of human beings through the early years of life has been followed by a few others. At first little attention was paid to the general questions of physiology. Lotze's Allgemeine Physiologic des korperlichcn Lebens (1851) was purely speculative, and treated physiological questions from the standpoint of philosophy ; nevertheless, it necessarily would have proved a valuable stimulus to the experimental physiology of that time in the investigation of important questions, if in exact science interest in general problems had been greater. Although the striking works of Charles Robin, Chimie, anatomigue et physiologique (1853) and Anatomic et physiologic cellulaire (1873), presented a coherent summary of the anatomy and physiology of the cell, unfortunately they were little appreciated from the physiological side.

So also the cell-pathological researches and ideas of Rudolf Virchow (Cellularpathologie, 1858), which quite overturned medical ideas, until very recently and in spite of their showing very clearly the enormous practical importance of general physiological researches upon the cell, have had scarcely the slightest influence upon the development of physiology, because the latter science was captivated by questions of a more special kind. More attention was excited by Claude Bernard's Lecons sur les phenomenes de la vie communs aux animaux et aux vegetanx (1878), which treated a number of general questions concerning life in a classic manner, although somewhat unequally. Preyer endeavoured to discuss the questions of general physiology more uniformly in his Elemente der allgemeincn Physiologic (1883), but unfortunately the book contains only a schematic summary of the subject. Finally, the researches of the histologists and the zoologists afforded many

contributions to the physiology of the cell, and in our own time, from this side especially, the physiology of reproduction, fertilisation, development, and heredity has been taken away from physiology proper, and developed into a fruitful and independent subject.1 The comparative method has not been employed in physiology since Johannes Miiller's time, unless the few researches that have been conducted upon other animals than the usual dogs, rabbits, and frogs are to be considered as comparative.

Plant physiology, however, has developed quite independently into a nourishing science ; and the distinguished labours of Hofmeister, Nageli, Sachs, Pfeffer, Strasburger, Berthold, and others have made this in recent times the most complete branch of physiology. This is due partly to the fact that all vital relations are much simpler and more easily surveyed in plants than in animals, and partly to the fact that plant physiology has made use of certain acquisitions of science that have thus far found little or no application to the physiology of animals.

There are three of the greatest discoveries of this century, from the further expansion of which physiology is justified in still expecting great results. One of these is the law of the conservation of energy, which was definitely expressed by Robert Mayer (1814-1878), and was established most comprehensively by Helmholtz. Modern chemical investigations had led to a recognition of the law of the conservation of matter, by showing that the quantity of matter, of atoms, in the universe is constant, and that the smallest atom cannot by any agency be destroyed or recreated. The law of the conservation of energy expresses the same fixedness for the sum of the energy of the universe. Energy, like matter, can be neither destroyed nor recreated ; when it seems to appear or disappear, it merely passes from one form into another. Among the recognised forms of energy two varieties are distinguished : energy of motion, or kinetic energy, when power is in action, i.e. is producing motion ; and energy of position, or potential energy, when it is latent but under certain conditions can come into action. Thus, e.g., the potential energy that was produced in the Carboniferous age by transformation of the kinetic energy of the sun's rays through the activity of plants and was stored up as chemical affinity in vast strata of coal, passes over into heat upon combustion of the coal. The heat is transformed by steam engines which are heated by the coal, into the energy of

1 Rdsumes of what has been accomplished in this field are given by the following books: Die, Zelle und die Gewebe, by O. Hertwig (1892) [authorised English translation, The Cell: Outlines of General Anatomy and Physiology, 1895]; Gesammelte Abhandlungen iiber EntwicUungsmechanik, by W-. Roux (1895); La structure du protoplasma et les theories sur Vheredite, etc., by Yves Delage (1895) ; [and The Cell in Development and Inheritance, by E. B. Wilson (1896)].