CHAPTER XX

RETROSPECT AND PROSPECT. RECENT TENDENCIES IN BIOLOGY

When one views the progress of biology in retrospect, the broad truth stands out that there has been a continuity of development in biological thought and interpretation. The new proceeds out of the old, but is genetically related to it. A good illustration of this is seen in the modified sense in which the theories of epigenesis and pre-formation have been retained in the biological philosophy of the nineteenth century. The same kind of question that divided the philosophers of the seventeenth and eighteenth centuries has remained to vex those of the nineteenth; and, although both processes have assumed a different aspect in the light of germinal continuity, the theorists of the last part of the nineteenth century were divided in their outlook upon biological processes into those of the epigenetic school and those who are persuaded of a pre-organization in the germinal elements of organisms. Leading biological questions were warmly discussed from these different points of view.

In its general character the progress of natural science has been, and still is, a crusade against superstition; and it may be remarked in passing that "the nature of superstition consists in a gross misunderstanding of the causes of natural phenomena." The struggle has been more marked in biology than in other departments of science because biology involves the consideration of living organisms and undertakes to establish the same basis for thinking about the organization of the human body as about the rest of the animal series.

The first triumph of the scientific method was the overthrow of authority as a means of ascertaining truth and substituting therefor the method of observation and experiment. This carries us back to the days of Vesalius and Harvey, before the framework of biology was reared. But the scientific method, once established, led on gradually to a belief in the constancy of nature and in the prevalence of universal laws in the production of all phenomena. In its progress biology has exhibited three phases which more or less overlap: The first was the descriptive phase, in which the obvious features of animals and plants were merely described; the descriptive was supplemented by the comparative method; this in due course by the experimental method, or the study of the processes that take place in organisms. Thus, description, comparison, and experiment represent the great phases of biological development.

The Notable Books of Biology and their Authors.--The progress of biology has been owing to the efforts of men of very human qualities, yet each with some special distinguishing feature of eminence. Certain of their publications are the mile-stones of the way. It may be worth while, therefore, in a brief recapitulation to name the books of widest general influence in the progress of biology. Only those publications will be mentioned that have formed the starting-point of some new movement, or have laid the foundation of some new theory.

Beginning with the revival of learning, the books of Vesalius, _De Corporis Humani Fabrica_ (1543), and Harvey, _De Motu Cordis et Sanguinis_ (1628), laid the foundations of scientific method in biology.

The pioneer researches of Malpighi on the minute anatomy of plants and animals, and on the development of the chick, best represent the progress of investigation between Harvey and Linnæus. The three contributions referred to are those on the _Anatomy of Plants_ (_Anatome Plantarum_, 1675-1679); on the _Anatomy of the Silkworm_ (_De Bombyce_, 1669); and on the _Development of the Chick_ (_De Formatione Pulli in Ovo_ and _De Ovo Incubato_, both 1672).

We then pass to the _Systema Naturæ_ (twelve editions, 1735-1768) of Linnæus, a work that had such wide influence in stimulating activity in systematic botany and zoölogy.

Wolff's _Theoria Generationis_, 1759, and his _De Formatione Intestinorum_, 1764, especially the latter, were pieces of observation marking the highest level of investigation of development prior to that of Pander and Von Baer.

Cuvier, in _Le Règne Animal_, 1816, applied the principles of comparative anatomy to the entire animal kingdom.

The publication in 1800 of Bichat's _Traité des Membranes_ created a new department of anatomy, called histology.

Lamarck's book, _La Philosophie Zoologique_, 1809, must have a place among the great works in biology. Its influence was delayed for more than fifty years after its publication.

The monumental work of Von Baer on _Development_ (_Ueber Entwicklungsgeschichte der Thiere_), 1828, is an almost ideal combination of observation and conclusion in embryology.

The _Microscopische Untersuchungen_, 1839, of Schwann marks the foundation of the cell-theory.

The _Handbook_ of Johannes Müller (_Handbuch der Physiologie des Menschen_), 1846, remains unsurpassed as to its plan and its execution.

Max Schultze in his treatise _Ueber Muskelkörperchen und das was man eine Zelle zu nennen habe_, 1861, established one of the most important conceptions with which biology has been enriched, viz., the protoplasm doctrine.

Darwin's _Origin of Species_, 1859, is, from our present outlook, the greatest classic in biology.

Pasteur's _Studies on Fermentation_, 1876, is typical of the quality of his work, though his later investigations on inoculations for the prevention of hydrophobia and other maladies are of greater importance to mankind.

It is somewhat puzzling to select a man to represent the study of fossil life, one is tempted to name E.D. Cope, whose researches were conceived on the highest plane. Zittel, however, covered the entire field of fossil life, and his _Handbook of Palæontology_ is designated as a mile-post in the development of that science.

Before the Renaissance the works of Aristotle and Galen should be included.

From the view-point suggested, the more notable figures in the development of biology are: Aristotle, Galen, Vesalius, Harvey, Malpighi, Linnæus, Wolff, Cuvier, Bichat, Lamarck, Von Baer, J. Müller, Schwann, Schultze, Darwin, Pasteur, and Cope.

Such a list is, as a matter of course, arbitrary, and can serve no useful purpose except that of bringing into combination in a single group the names of the most illustrious founders of biological science. The individuals mentioned are not all of the same relative rank, and the list should be extended rather than contracted. Schwann, when the entire output of the two is considered, would rank lower as a scientific man than Koelliker, who is not mentioned, but the former must stand in the list on account of his connection with the cell-theory. Virchow, the presumptive founder of pathology, is omitted, as are also investigators like Koch, whose line of activity has been chiefly medical.

Recent Tendencies in Biology. Higher Standards.--In attempting to indicate some of the more evident influences that dominate biological investigation at the present time, nothing more than an enumeration of tendencies with a running commentary is possible. One notes first a wholesome influence in the establishment of higher standards, both of research and of scientific publication. Investigations as a whole have become more intensive and more critical. Much of the work that would have passed muster for publication two decades ago is now regarded by the editors of the best biological periodicals as too general and too superficial. The requisites for the recognition of creditable work being higher, tends to elevate the whole level of biological science.

Improvement in Tools and Methods.--This has come about partly through improvement in the tools and in the methods of the investigators. It can hardly be said, however, that thinking and discernment have been advanced at the same rate as the mechanical helps to research. In becoming more intensive, the investigation of biological problems has lost something in comprehensiveness. That which some of the earlier investigators lacked in technique was compensated for in the breadth of their preliminary training and in their splendid appreciation of the relations of the facts at their disposal.

The great improvement in the mechanical adjustments and in the optical powers of microscopes has made it possible to see more regarding the physical structure and the activities of organisms than ever before. Microtomes of the best workmanship have placed in the hands of histologists the means of making serial sections of remarkable thinness and regularity.

The great development of micro-chemical technique also has had the widest influence in promoting exact researches in biology. Special staining methods, as those of Golgi and Bethe, by means of which the wonderful fabric of the nervous system has been revealed, are illustrations.

The separation by maceration and smear preparation of entire histological elements so that they may be viewed as solids has come to supplement the study of sections. Reconstruction, by carving wax plates of known thickness into the form of magnified sections drawn upon their surfaces to a scale, and then fitting the plates together, has been very helpful in picturing complicated anatomical relations. This method has made it possible to produce permanent wax models of minute structures magnified to any desired degree. Minute dissections, although not yet sufficiently practiced, are nevertheless better than the wax models for making accurate drawings of minute structures as seen in relief.

The injection of the blood-vessels of extremely small embryos has made it possible to study advantageously the circulatory system. The softening of bones by acid after the tissues are already embedded in celloidin has offered a means of investigating the structure of the internal ear by sections, and is widely applicable to other tissues.

With the advantage of the new appliances and the new methods, the old problems of anatomy are being worked over on a higher level of requirement. Still, it is doubtful whether even the old problems will be solved in more than a relative way. It is characteristic of the progress of research that as one proceeds the horizon broadens and new questions spring up in the pathway of the investigator. He does not solve the problems he sets out to solve, but opens a lot of new ones. This is one of the features of scientific research that make its votaries characteristically optimistic.

Experimental Work.--Among the recent influences tending to advance biology, none is more important than the application of experiments to biological studies. The experimental method is in reality applicable to diverse fields of biological research, and its extensive use at present indicates a movement in the right direction; that is, a growing interest in the study of processes. One of the earliest problems of the biologist is to investigate the architecture of living beings; then there arise questions as to the processes that occur within the organism, and the study of processes involves the employment of experiments. In the pursuit of physiology experiments have been in use since the time of Harvey, but even in that science, where they are indispensable, experiments did not become comparative until the nineteenth century. It now appears that various forms of experiment give also a better insight into the structure of organisms, and the practice of applying experiments to structural studies has given rise to the new department of experimental morphology.

For the purpose of indicating some of the directions in which biology has been furthered by the experimental method of investigation, we designate the fields of heredity and evolution, changes in the environment of organisms, studies on fertilization and on animal behavior.

The recognition that both heredity and the process of evolution can be subjected to experimental tests was a revelation. Darwin and the early evolutionists thought the evolutionary changes too slow to be appreciated, but now we know that many of the changes can be investigated by experiment. Numerous experiments on heredity in poultry (Davenport), in rats, in rabbits, and in guinea-pigs (Castle) have been carried out--experiments that test the laws of ancestral inheritance and throw great light upon the questions introduced by the investigations of Mendel and De Vries. The investigations of De Vries on the evolution of plant-life occupy a notable position among the experimental studies.

A large number of experiments on the effects produced by changes in the external conditions of life have been made. To this class of investigations belong studies on the regulation of form and function in organisms (Loeb, Child), the effects produced by altering mechanical conditions of growth, by changing the chemical environment, etc. There is some internal mechanism in living matter that is influenced by changes in external conditions, and the study of the regulation of the internal processes that produce form and structure have given rise to a variety of interesting problems. The regeneration of lost parts and regeneration after intentionally-imposed injury has received much attention (Morgan). Marine animals are especially amenable to manipulations of this nature, as well as to alterations in their surroundings, on account of the ease in altering the chemical environment in which they live. The latter may be accomplished by dissolving harmless chemical salts in the sea-water, and observing the changes produced by the alterations of the surrounding conditions. By this means Herbst and others have produced very interesting results.

In the field of artificial fertilization, free swimming larvæ have been raised from eggs artificially fertilized by changes in osmotic pressure, and also by treating them with both organic and inorganic acids; and these studies have greatly altered opinion regarding the nature of fertilization, and of certain other phenomena of development.

Animal Behavior.--The study of animal behavior (Jennings) is a very characteristic activity of the present, in which certain psychological processes are investigated. These investigations have given rise to a distinct line of research participated in by psychologists and biologists. The study of the way in which animals will react toward light of different colors, to variations in the intensity of light, to alterations in temperature, and to various other forms of stimuli are yielding very important results, that enable investigators to look beneath the surface and to make important deductions regarding the nature of psychological processes.

A line closely allied to experimentation is the application of statistics to biological processes, such as those of growth, stature, the law of ancestral inheritance, the statistical study of variations in spines, markings on shells, etc., etc., (Galton, Pearson, Davenport).

Other branches of biology that have been greatly developed by the experimental method are those of bacteriology and physiological chemistry. The advances in the latter have greatly widened the horizon of our view regarding the nature of vital activities, and they compose one of the leading features of current biological investigation.

Some Tendencies in Anatomical Studies. Cell-Lineage.--While experimental work occupies the center of the stage, at the same time great improvements in morphological studies are evident. It will be only possible, however, to indicate in a general way the direction in which investigations are moving. We note, first, as in a previous paragraph, that the improvement in morphology is generic as well as specific. Anatomical analysis is being carried to its limits in a number of directions. The investigations that are connected with the study of cells afford a conspicuous illustration of this fact. Studies in cell-lineage have led to an exact determination of cell-succession in the development of certain animals, and such studies are still in progress. Great progress also has been made in the study of physical structure of living matter. The tracing of cell-lineage is a feat of remarkably accurate and patient work. But, however much this may command our admiration, it has been surpassed (as related in