Part 30

An instrument invented by Ludwig is the mercurial blood-pump, the purpose of which is to separate from a known quantity of blood, derived directly from the circulation, the mixture of gases which it yields to a vacuum. This is an indispensable apparatus for the investigation of the physiology of breathing.

Ludwig devoted much attention to the physiology of secretion. Here his work has been of great importance in connection with the time-honored discussion between the ‘vitalists’ and the ‘mechanists’. He succeeded in showing that the process of secretion can be so transformed experimentally as to do external mechanical work. This was victory for the mechanist theory. The idea has since been applied to many structures.

It is impossible to attempt here any general summary of the conclusions reached by physiological research since Ludwig. Some have affected the actual practice of Medicine. Others are too recent or too little certain to have reacted in this manner. It is, however, safe to say that the more important conclusions of the three modern founders of the science, Müller, Bernard, and Ludwig, form the main scientific background of the clinical practice of our time. The results of the movement that they represent, together with the knowledge of the cellular structure of the body (§ 5, p. 219) and of the life-histories of the disease-causing organisms (§ 6, p. 224), are the three main groups of ideas which separate the physician of our day from Laënnec (p. 161).

The cylinder H turns with the axis AB on which it is rigidly fixed. It is rotated by a handle at A which raises the weight C. When the weight is allowed to fall the cylinder rotates automatically. The rest of the apparatus is devised to secure constancy in rate of rotation. This was done by utilizing the effects of centrifugal force.

(As the rate of rotation increases the pendula D and E fly apart, they separate the weights F and G. These move with friction which increases as they separate, thus decreasing the rate of rotation.)

The movements of the pen at K are transferred into permanent graphic form by writing on the rotating cylinder H.

§ 5. The Cell Theory and Cellular Pathology.

During the process of the microscopic analysis of plants that took place in the seventeenth century a number of observers distinguished the walls of plant-cells and the word cell was introduced into the English language. Less clearly, a similar structure was discerned in animals. No real understanding of the nature of cells was, however, reached. Little farther progress was made in the eighteenth century, but just at its close a young French microscopist, Marie François Xavier Bichat (1771-1802), likened the microscopic structure of the animal body to the substance of a woven fabric. The word he used was the old French term tissu. He perceived that the different parts of the body, bones, muscles, nerves, blood-vessels, and the like, each presented a characteristic microscopic pattern. According to these appearances he analyzed the parts of the body into twenty-one ‘tissues’. Study of this kind came to be called ‘Histology’ (Greek histos = web).

During the seventeenth, eighteenth, and early nineteenth centuries, some advances were made in the knowledge of those organisms whose bodies are made up of only one cell, but their essential nature was still unappreciated. In the early nineteenth century a number of botanists and others were observing cells and cell contents. But no important advance in the interpretation of the appearances was made until the matter was taken up by Schleiden.

Matthias Jakob Schleiden (1804-81), professor at Jena in 1838, put the matter in a new light. He noted, as had certain of his predecessors, the constant presence in every cell of the structure we now call the ‘nucleus’, and came to the conclusion that it is essential to the life of every cell. He reached the conception, moreover, that in a multi-cellular organism, such as a tree, every cell has a double life, one an essential and independent one, pertaining to its own development alone, the other an incidental and dependent one, in so far as it is an integral part of the plant. His work was somewhat vitiated by a fanciful conception of the origin of new cells.

The work of Schleiden was amplified and corrected in 1839 by Theodor Schwann (1810-82), a pupil of Müller. He showed that the tissues of animals, like those of plants, are susceptible of analysis into cells, and the difficulty of this process arises from the extreme modification of such cells as have developed for various special purposes. He showed too that the ovum or egg of animals is, in the first instance, a single cell, and that the cells of the body are derived and descended from it. He demonstrated that the entire animal or plant body is composed either of cells or of substances that are excreted or thrown off by cells. He gained some insight into the life of animal cells and in doing so he invented the very useful word metabolic. The word means ‘liable to change’. It was used by Schwann, and is still habitually used in modern Medicine to indicate chemical changes within the body which are specially associated with living activity.

Contributions to the cell theory were made by other botanists. Hugo von Mohl of Tübingen (1805-72) distinguished the contents of the vegetable cell just under the cell-wall from the watery sap that fills the interior, introducing for it the term protoplasm (1846). The Swiss, Karl v. Nägeli (1817-91), by chemical examination proved that protoplasm is nitrogenous and differs from other cell constituents (1862).

The cell theory was placed on a firm and clear footing by Max Schultze (1825-74), successor of Helmholtz (p. 213) as professor of Anatomy at Bonn. He defined the cell as ‘a lump of nucleated protoplasm’ (1861), introduced the idea of protoplasm as ‘the physical basis of life’, and showed that it presented essential similarities, physiological and structural, whether in plants or animals, and whether in higher or lower forms.

The study of tissues, Histology, was raised to the status of an independent science by the Swiss, Albrecht von Kölliker (1817-1905), pupil of Müller and professor at Würzburg, who wrote the first text-book on the subject (1850-52). Apart from this achievement, Kölliker is remarkable for having reached some of the conclusions in connection with heredity that are associated with the name of Mendel, of whose work he knew nothing.

Even more influential on medical thought than Kölliker was Rudolf Virchow (1821-1902) of Berlin, one of the leading names in modern Medicine. There is indeed hardly any department of medical thought that has not gained something from Virchow’s work. His great achievement is the way in which he carried the Cell Theory into the analysis of diseased tissues. In his Cellular Pathology (1858) he analyzes diseased tissues from the point of view of cell formation and cell structure. Important sections of the science of Cellular Pathology have been explored so well by Virchow that they have been little extended by his successors. He initiated the familiar idea that the body may be regarded as ‘a cell State in which every cell is a citizen’. Disease is often but a civil war. The white blood corpuscles, which have the power of engulfing and rendering innocuous bacteria and other foreign bodies, have been compared to police or scavengers. In some respects Virchow was strangely conservative, and notably he opposed the evolutionary view of the origin of living forms. Virchow’s conceptions of the functions of the white blood corpuscles were largely extended by the Russian biologist Élie Metschnikoff (1845-1916) and the English worker Almroth Wright (1861-).

Since Virchow and Kölliker the study of the intimate structure and workings of the cells themselves, as distinct from the tissues, has become a separate and independent science under the name of Cytology. It may even be extended to the study of cells in disease as Cyto-Pathology.

Among the major developments of Cellular Pathology and Cyto-Pathology is the study of abnormal ‘new growths’. The most malignant types of these belong to the group known as the ‘Cancers’. The occurrence of most of these becomes more frequent as life advances (Fig. 135). Their cytological features are now well known. A cancer consists essentially of an increase of cellular tissue, following abnormally rapid multiplication of one type of cell. The new growth is equipped with a blood-supply which enables it to increase at the expense of other tissues and regardless of their needs.

Cancers almost always arise at one point, and are very seldom multiple in origin. It is fairly established that they are not infectious or contagious, and there is no very satisfactory evidence that a tendency to them is inherited. Our scientific knowledge of Cancers is largely derived from animals. Cancers are ‘specific’ in the sense that those of one animal species will not grow when inoculated into another species. An immense amount of work has been done on inoculated Cancers, but it has become evident that some physiological factor is involved in Cancer incidence such that an inoculated Cancer is not entirely comparable with so-called ‘spontaneous’ Cancer. As to what that physiological factor can be we are still in the dark.

Although we know nothing effective as to this physiological factor, yet experiments in the artificial production of Cancer, apart from inoculation, have been attended with success. That various forms of chronic irritation are associated with the onset of Cancer has long been clinically recognized. It has been found possible to reproduce experimentally this relation between irritation and new growth, and so, for example, to induce Tar Cancer in mice. Nevertheless, it must be admitted that Cancer investigation is in an unsatisfactory state, and has yielded fewer positive results than any other department of Pathology of comparable importance. It is possible that we do not yet know enough of normal Cell Physiology to investigate with profit the forms of cellular perversion known as Cancer.

Drawings by Theodor Schwann to illustrate the nature and origin of animal cells. All are highly magnified.

FIG. 102. The first step in the origin of cartilage from cellular tissues. At the lower part the young cells are without cell-walls. In the upper part they have formed walls and are beginning to secrete cartilaginous substance. Nuclei and nucleoli are clearly visible.

Above is shown a piece of maturer cartilage, in which the cells are imbedded in a mass of cartilaginous material.

FIG. 103. Pigment cells, such as are characteristic of the skin of the frog. In the lowest cell, which is contracted, the nucleus is concealed by the pigment. The upper two are more expanded and in them nuclei can be seen.

FIGS. 104 & 105 show how structures of very diverse form can be differentiated from cells of the same type.

FIG. 104. Young cells from a developing feather. These cells may enlarge, secrete hard walls, and form the fine spongy tissue of the inner part of the shaft of the feather. Or the cells may elongate, the protoplasm become granular, and finally break up into fibers (Fig. 105). These form the tough fibrous matter of the outer part of the shaft of the feather. In either case, the nucleus disappears and the cell dies.

§ 6. Establishment of the Doctrine of the Germ Origin of Disease.

The view that many diseases, especially those of a contagious or infectious nature, originate from the invasion of the body by special organisms and their multiplication within the body, came into prominence in the second half of the nineteenth century. There had been many previous adumbrations of this view and, in its final establishment, more than one hand may be discerned. Above all others who have worked in this field towers the mighty figure of Louis Pasteur (1822-95). We shall do no grave injustice to any man if we treat the scientific demonstration of the doctrine as the product of his superb genius.

The opening of Pasteur’s interest in disease can be seen in his work on fermentation. At first he was faced with the opposition of Liebig. According to that eminent chemist, fermentation was not the result of vital activity but was a purely chemical change (p. 207). A ferment he regarded as an unstable organic product, the character of which determined the manner of decomposition of the medium in which it is placed. Pasteur demonstrated that, as there is a specific alcoholic ferment, so there is a specific milk-souring ferment. Any nitrogenous matter present in a fluid containing it will serve as food for the development of a ferment, but will not of itself induce fermentation. Ferments have, he demonstrated, the power of reproduction. Pasteur rapidly seized on the idea of the specificity of ferments. An albuminous sugar solution can be converted into various products by the addition of various ferments. According as one sows, so will one reap. The milk-souring ferment, Pasteur concluded, is organized and living, and its action is correlated to its development and organization. No life, no ferment; no ferment, no fermentation.