THE PHYSIOLOGICAL LAWS OF HUMAN INCREASE. THERE is no science whose history presents discoveries more brilliant or important than that of physiology. And though they have not been confined to any one period or nation, most of these discoveries have been made in the present century. While Hippocrates and Galen gained in their day great celebrity in this field of inquiry, physiology as a science may with propriety be said to have received its starting point only two centuries ago from that immortal discovery by Harvey of the circulation of the blood. Soon after this, the inductive principles of philosophy were introduced by Lord Bacon, when all vital phenomena were brought to the test of observation and experiment. Here, by applying the inductive method of investigation, Haller made greater advances in this science than any other individual, so much so that he has been termed the "Father of Modern Physiology." But within the present century, by means of chemistry and the use of the microscope, with their appliances, still greater and more surprising advances have been made in a knowledge of physiology. In fact, the last forty or fifty years have witnessed here a continued series of new and valuable discoveries; and, while most of them have been applied with direct reference to improvement in medicine and the healing art, some have a far higher, broader, and more important bearing upon human welfare. This science unfolds not only the great laws of life and health, but involves principles that lie at the foundation of all true education, as well as of permanent improvement in civilization. Judging from the past history of discoveries in this and kindred departments of inquiry, it is to be presumed there are still great truths and laws existing in physiology that have never yet been brought to light. Some of its most distinguished cultivators speak of the science as being yet in its infancy, and of "the rich harvest which awaits the physiological laborer." Says one: "Certainly a well-arranged and most comprehensive science has already been reared, but it is destined to attain proportions much more gigantic than it now presents." If the theory of human increase about to be proposed is found to have a sure basis in the great laws of Physiology, it will be difficult to find language adequate to express the value of the principles involved, or the extent of their application. It approaches the subject from a point of view which has not hitherto been taken, and which opens a field of inquiry so new, so vast, and so complicated, that one almost shrinks from the undertaking. The most that any single individual can do in such a field, is to throw a mere pebble into the great ocean of truth. In entering, therefore, upon an examination of this question, it becomes the inquirer to suspend his opinion till he can obtain a sufficient accumulation of facts and knowledge on the subject, so that he can form some rational and correct judgment as to their relative bearing, and the support they give to this or that theory. No prejudice or pre-conceived opinions should be allowed to stand in the way of coming to a fair and intelligent decision. But, in order to do this properly, some general knowledge—and the more profound the better-of the facts and laws of physiology is indispensable. Guided by the true Baconian spirit of philosophy, and after a thorough investigation of the whole subject, it may be expected we shall then arrive at some enlightened and satisfactory results in the extensive field of investigation. The main reason why this most important subject—the law of human increase or of population-has not created more general interest, or found a more exact and uniform support is, that the true basis upon which the Creator placed it, has in a great measure been overlooked. It is a singular fact, that among all the writers on this subject there is scarcely one who has been thoroughly educated in the science of physiology, or in the practical application of medicine to the laws of life. The strictly inductive method by which the great principles of science are established has been but little employed. The attention of those who have made investigations and written most extensively upon this subject, has been turned in almost every other direction in quest of some cause, agency, or influence to explain changes in population, rather than of any primary fundamental law in human organization itself. But it stands to reason and common sense, that the organs of the body, whose functions perform so important an agency in this matter, must be governed by some fixed laws as a part or condition of their creation. The existence of such laws is traceable throughout the works of the Creator, wherever science has pushed her researches, and especially in the animal and vegetable kingdoms. The human system cannot be made an exception to this universal principle. This law of propagation-the most important of all-must constitute a part of the nature of every organized body in its creation, though in its operations it may be affected by extraneous causes and influences. However powerful may be the effect of climate, food, and other external agents upon the application or working of this law, whether to impede, thwart, or in any way modify its operation, the la'v itself must exist in the body, and in a great measure control it. The truth of this fact is strikingly illustrated in the changes that have taken place in domestic animals. Within fifty years, or even twenty-five, what a wonderful improvement has been made, especially in the case of the horse, the cow, the sheep, etc. While external agents have had great influence in these changes, the most important agency of all—the leading factor employed-has been found to exist in the organization itself. From the intimate analogy of law, as applied to animal and human physiology, and from the fact that physicians, as a class, spend most of their lives in the study of the body, it seems somewhat strange, at first, that their attention has never been turned more in this direction. But this ground has for a long time been pretty thoroughly occupied by writers upon population in attributing the causes or law of its increase to other sources than to the body. Besides, the attention of the medical profession, as far as turned in this particular direction, has been almost exclusively devoted to the reproductive organs-dwelling not so much upon their structure or functions in establishing any law, as upon certain normal or morbid conditions; whereas both the anatomy and physiology of these organs are very much dependent upon, as well as affected by, the development, health, and other conditions of all parts of the system. Another reason for this omission may have arisen from the fact, that the laws of hereditary descent, when considered in all their extent and effects, constitute a new chapter comparatively in physiology. If a thorough exposition of this particular department of the science in all its bearings could have. been made, or attained, the idea would almost naturally have |