The third class, who take such delight in minimizing the achievements of the physiologist, usually are found, if anyone takes them seriously, to know very little either about the science of physiology itself or the history of its growth. I leave the reader to form his own verdict upon the value of the results obtained from their exceedingly brief and sketchy description in this little volume, with the remark that the science is barely more than three-quarters of a century old, and the most important additions to our knowledge have been made within the last twenty years. There were, paradoxical as it may sound, great physiologists before then; the work of Harvey, who three centuries ago discovered the circulation of the blood, is above all praise; but how nebulous must have been their ideas may be seen from the following facts: It was only at the beginning of the nineteenth century that the atomic theory of matter was formulated; it was not until twenty years later that the world was startled by a daring chemist who showed that organic compounds obeyed the same natural laws as inorganic; and not until ten years later was the cellular structure of animals, the groundwork in all study of life, recognised. Even when the science was set upon firm foundations, progress was at first necessarily slow: the organic chemist took some time in examining and classifying the compounds met with in the body—he has not finished yet; and even when the cell theory was grasped, it required much ingenuity and long patience to devise ways of examining organs under the microscope, so that their structure could be made out. The microscope itself was a poor toy fifty years ago, magnifying a diameter ten times where now it magnifies a hundred, and giving only a dim and distorted image. The perfecting of the microscope, and the introduction of anæsthetics and antiseptics, have led to enormous strides being made within the last two decades. The result of the advance in chemical knowledge, and the introduction of fresh aids to investigation, led to the discarding of vital force as a working hypothesis. Vital force was the bane of the earlier biologists. They made it accountable for all they could not understand, and with this restatement of their difficulties—a restatement which they called an explanation—refrained from further research. But when it was found that many of these inexplicable phenomena, though refractory, yielded to careful study, and could be explained by chemical and physical laws, the physiologist ceased to say of them, ‘They are problems connected with Life, and therefore explained by Vital Force, which is past man’s understanding,’ and frankly admitted that there were many things which he did not as yet fathom. Recently a vitalistic school has cropped up again, declaring that all that it cannot understand must infallibly be due to some occult agency. It shows remarkable vitality in surviving the shocks of successive discoveries.