A Manual of Physiology

HE word "physiology," or "physiological science," is diffi cult to define. According to its etymology we should interpret it as the science of life or animation (que). The word "life" or "animation" characterizes the phenomena which exist in a living being. These phenomena are quite complex, and the history of science presents a crowd of definitions, all of which are influenced by the inadequate state of the knowledge resulting from observation at different periods.

If, in the actual state of our anatomical knowledge, we examine the organic elements of a living being, we find that by their aspect alone we can divide these into two classes. One class is thus represented by the purely mechanical (vessels, fibres) or chemical office (different fluids) which these elements must render to the organism. Those of the second class appear to us at first inexplicable (globular forms, cells 2), if we consider their functions either as mechanical or chemical.

If, on the contrary, we examine the acts of which the living being is the theatre, we meet a great number of physical and

1 An attempt has been made to substitute for the word "physiology" that of "biology," which, by its etymology, does not signify science of life, but the different phases of life.

2 We purposely employ the words "cell" and "globules indifferently, though we own to our preference for the word "globule.

chemical phenomena resembling in every respect those produced by inanimate nature: thus, the eye is a physical and dioptric apparatus; the transformation of starch into sugar, in the mouth, is a purely chemical fact. But we meet, besides these, phenomena which can be explained neither by chemistry nor by physics: these phenomena deserve a separate study, and should constitute a special science in a department whose bounds are unlimited.. Such phenomena are, properly speaking, vital: but at this present time we can only give a purely negative definition of life; viz., life is all that cannot be explained by chemistry or by physics.

But, whilst all the chemical and physical phenomena are localized in those portions of the apparatus that are simply mechanical or non-globular (fibres, vessels, etc.); whilst these apparatus present to us always the same essential aspect, and whilst, for example, a fibre taken all by itself can often offer no characteristic features by which we can designate it as young or old, yet the phenomena which are neither chemical nor physical, in other words, vital phenomena, are localized in the globules or cells, so far as we can now by the process of elimination suppose; this is also confirmed by observation; these elements are presented to our view as continually undergoing changes; possessing an ephemeral existence they undergo metamorphoses of form and of composition, from the moment which we can call their time of birth to that which constitutes the time of death; in short they are endowed with age. This is precisely the essence of those phenomena which can be explained neither by chemistry nor by physics, so that we can say life is the correlation of successive phenomena presented by the globular element, and can define in a positive manner the word physiology, as the study of the globular element in its metamorphoses. Physiology in its essence can to-day be no more than cellular.

These metamorphoses are, as we have said, "changes of form and composition." Changes of composition are not necessary to characterize life, for every organic body in contact with the air will absorb oxygen and evolve carbonic acid, until it may have become burnt up or putrid. The globule, however, far from being destroyed by this change, is transformed, is multiplied. This represents its life. Cuvier defines this "un tourbillon " (vortex),- rather an incomplete definition, because, laying aside the changes of form, it can

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A Manual of Physiology: Being a Course of Lectures