An American text-book of physiology / by Henry P. Bowditch [and others]., edited by William H. Howell.

William Henry Howell

Date:: 1897

Credit: An American text-book of physiology / by Henry P. Bowditch [and others]., edited by William H. Howell. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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$j)lanation. Most |)liy.si()l()i!;i.sts unquestionably believe that lurther experi- nientiil work will bring this })henonienon out of its obscurity and show that it is explicable in terms of known physical and chemical forces acting through the peculiar substance of the absorptive cell. The i'acts of heredity and consciousness offer difficulties of a much graver character. The function of reproduction is two-sided. lu the first ])lace there is an active multiplication of cells, beginning with (he segmentation of the ovum into two blastomeres and continuing in the lai-gcr animals to the formation of an iniuunerable multitude of cellular units. In the second jilace there is ])resent in the ovum a form-building j)o\ver of such a character that the great complex of cells arising from it form not a heterogeneous mass, but a definite organism of the same structure, organ for organ and tissue for tissue, as the parent form. The ovum of a starfish develops into a starfish, the ovum of a dog into a dog, and the ovum of man into a human being. Herein lies the great problem of heredity. The mere multiplication of cells bv direct or indirect division is not beyond the range of a conceivable me- chanical explanation. Given the properties of assimilation and contractility it is possible that the act of cell-division may be traced to purely physical and chemical causes, and already cytological work is opening the way to credible hvpotheses of this character. But the phenomena of heredity, on the other hand, are too complex and mysterious to justify any immediate expectation that they can be explained in terms of the known properties of matter. The crude theories of earlier times have not stood the test of investigation by modern methods, the microscopic anatomy of both ovum and sperm showing that they are to all api)earauces simple cells which exhibit no visible signs of the wonderful potentialities contained within them. Histological and experi- mental investigation has, however, cleared away some of the difficulties for- merly surrounding the subject, for it has shown with a high degree of prob- ability that the power of hereditary transmission resides in a ])articular sub- stance in the nucleus, namely in the so-called chromatin material which forms the chromosomes. The fascinating observations which have led to this con- clusion promise to open up a new field of experimentation and speculation. It seems to l)e possible to study heredity by accepted scientific methods, and we may therefore hope that in time more light will be thrown upon the conditions of its existence and possibly upon the nature of its activity. In the facts of consciousness, lastly, we are confronted with a problem seemingly more difficult than heredity. In ourselves we recogni/e difierent states of consciousness following upon the physiological activity of certain parts of the central nervous system. We know, or think we know, that these so-called p.sychical states are correlated with changes in the ])rotoplasmic material of the cortical cells of the cerebral hemispheres. When these cells are stimulated, psychical states result; when they are injured or removed, psychical activitv is depressed or destroyed altogether according to the extent of the injury. From the physiological standpoint it would seem to be as justifiable to assert that consciousness is a property of the cortical nerve-cells$

An American text-book of physiology / by Henry P. Bowditch [and others]., edited by William H. Howell.

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