Page:Mind (New Series) Volume 9.djvu/341

VITALISM: A BRIEF HISTOKICAI, AND CRITICAL KKVIKW. .i-J7 gemmules of Darwin, or the ids and idents of Weismann. The efforts to attribute vital properties to microscopic intrn- cellular particles result in a very close imitation of van Helmont's theory, a red net io ad ab^ iifficiently obvious. Every particle, every cell, every tissue, every organ, nay, also the whole organism, each must have its appropriate vital force or system of vital forces. Such a difficulty will be avoided if it be remembered that life is the result of the interaction of various substances, and hence is capable of existence only in relatively large quantities of matter (26). The following considerations make it sufficiently obvious that protoplasm has by no means universal characters. The life of a plant is very different from that of an animal ; and , as plant and animal may develop under similar external circumstances, the differences in metabolism and in general activity must reside in protoplasm itself. The egg of a fowl cannot be made to develop into a horse. Temperament and constitution in one man are not the same as in his neighbour. Clearly the characters of living organisms are very various, and presumably they are associated with corresponding dif- ferences in the chemical constitution and composition of the substance of those organisms. It is at the same time to be remembered that profoundly different results may be obtained by subjecting one and the same protoplasm to different external forces. A given bud may be made to develop at will into a vegetative or a floral shoot or into a thorn, while a dioecious plant has apparently been made to develop a preponderance of male or female flowers. A similar influence of external conditions on growth is again shown in the case of lateral shoots, the growth of which is clearly correlated with the degree of development of the axial bud. All these phenomena receive the same definite explanation at Weis- mann's hands. However, the recent researches of Oscar Hertwig (27) in experimental embryology, if accepted, show that Weismann's theory of determinants must be modified. To account for the " isotropy " of protoplasm, either every cell of a developing vertebrate-ovum must (until the formation of the notochord) be credited with sufficient ids to produce any organ of the mature body ; or Hertwig's theory must be adopted that development and evolution result not only from the nature of the germinal material, but from the moulding influence of growth, and from the relation of cells to their external and internal environment. The following experiment which demonstrates the educational capacity of protoplasm is suggestive. If transferred by easy and gradual stages from a normal to a fairly strong poisonous fluid,