were exposed, vivisection did not render so clear the secretory activities of the glands, the changes brought about by digestion, the intricacies of tissue nutrition, and the workings of the nervous system. These physiological problems were more intimately connected with the living material, and were not so open to such observation or experimental enquiry as was then possible. And it may be said that less even was known of the structure of the organs concerned in these functions than there was of the circulatory and respiratory systems. But, Malpighi and his fellows showed the way to what was wanted, and, as will appear, the uses and workings of the structures became open to scientific enquiry with important consequences.
Mention must be made however in further illustration of my theme of what had been done to provide truer conceptions of the nature of muscular action. Up to the time of Vesalius and even for some time afterwards the contractile power of the muscles was regarded as resident in the connective tissue sheath of the fibres, the true muscle substances being looked upon as packing. Vesalius first indicated the proper rôle of this material, but it was not until more than a century later, in 1664, that Nicolas Stensen a Dane, described (1664–1667) the structure of muscular tissue as he had studied it with the
