Comparative Physiology
None of the experimental fields has been of greater importance in zoological progress than that which concerns the functions of the various organs. Without this companion science morphology and comparative anatomy would have become unintelligible. American investigators, among whom G. H. Parker stands prominent, have taken a leading part in this field also.
Neurology.—The physiological analysis of the components of the nervous system, both in vertebrates and invertebrates, is another important branch of experimental biology. The 28 volumes of the Journal of Comparative Neurology attest the large influence that American investigators have had in the development of this science.
Regeneration.—Experimental studies on the powers of regeneration in plants and animals have been made from the earliest times. During the past few years, however, there has been made a concerted attempt to analyze the factors which determine the amount and rate of regeneration. Much progress has been made toward the postulation of definite laws applicable to the regenerative processes of the parts of each organism. The critical analyses of Morgan, Loeb and Child have been particularly stimulating.
Tissue Culture.—Another line of experimental work which has been developed within the past few years by Harrison, Carrell, and others is the culture of body tissues in artificial media. These experiments have included the cultivation in tubes or on glass slides of the various tissues of numerous species of animals. They have yielded much information regarding the structure, growth and multiplication of cells, the formation of tissues, and the healing of wounds.
Transplantation and Grafting.—Closely associated experiments consist in the transplantation of organs or other portions of the body to abnormal positions, to the bodies of other animals of the same species or of other species. In this way much has been learned about the potentiality of organs for self-differentiation, for regulation, for regeneration and for compensatory adaptations. The experiments have shown, further, the independence of soma and germplasm and have revealed the nature of certain organs whose functions were previously obscure.
Tropisms and Instincts.—Another field of experimental biology concerns the analysis of behavior of organisms in response to various forms of stimuli. These studies are being prosecuted on all groups of organisms, including the larval stages of many animals, and are yielding most remarkable results. The success in this field of research is largely due to stimulating influence of Jacques Loeb, Parker, Jennings, and their co-workers.
Biological Chemistry.—Still another experimental field which has developed into one of the most important of the biological sciences relates to the fundamental chemical and physical changes which underlie all organic phenomena. A knowledge of both physiological and physical chemistry is to-day essential for all advanced biological work. The peculiar nature of life itself, of growth, disease, old-age, degeneration, death and dissolution are presumably only manifestations of chemical and physical laws. The ultimate goal of all experimental biology, therefore, will be reached only when the basic physico-chemical properties of life are understood. At that time only will the perennial controversy between vitalism and mechanism be ended.