formed from the segmentation globules, but never without previous impregnation. Sixth-There are three layers in the germinal membrane-external, internal, and middle. Seventh-From the external layer are developed the central nervous system, with all its connecting nerves—the retina (crystalline lens, choroid coat of the eye), the skin with all its appendages, such as glands, hair, nails, etc., and a part of the amnion. From the middle layer are developed the heart and all the vessels of the body, with all the muscles and bones and their connecting tissues. From the internal layer is formed the lining to all the mucous membranes of the body. Eighth-In tracing the development of the higher classes of animals, we have manifest indications of the types of structure of the classes below each of these higher. Ninth-These types of structure appear in the same order of succession in the embryo, as the class of animals which they typify appeared in their maturity at different periods of the earth's history. From these propositions, which have been clearly demonstrated, it is easy to see that embryology must be the guide in all attempts at the true system of classification, and that it is only by the study of the embryological development of the different organs and tissues, in the different classes of animals, that a true comprehension of their functions and relations can be obtained. Not only is this true in regard to anatomy and physiology, the foundation of all medical studies, but embryology must throw much light on pathological formations, on hereditary diseases, congenital deformities, prenatal influences, and many other subjects of the greatest practical importance to every scientific mind, especially so to every conscientious physician. It is to be hoped that our Universities and Medical Colleges will soon consider embryology worthy of more consideration than has yet been given, and our young stu dents will take advantage of this field for original research and important discoveries, and thus aid in perfecting this, as yet, young science. Text books on this subject are few. Kölliker and Schenck have published small works on this subject in the German language, but I know of no other works attempting to give a general sketch even of the science as it now exists. Many valuable monographs are scattered through the scientific journals of Europe and America, awaiting some master hand to bring them together. Whoever has time to search for them will find it a most fascinating employment, and will be astonished at the amount of labor done by men whose names, like that of Mons. Gerbe of Paris, are seldom seen or heard, yet are worthy of the highest respect and honor. They work from a love for science and a desire to add to the general fund of knowledge for the world's benefit. ON MENTAL INFLUENCES. By G. W. DAVIS, M. D., OF CHICO. Every period of human life, from cradled infancy to the infirmities that pave the path of second childhood, is surrounded by numberless objects, circumstances, and influences that make deep and abiding impression upon the mind. The multiplicity of subjects in the different kingdoms of nature, and the ever varying interests and objects by which man is surrounded, and with which he is daily and hourly in contact, invigorate his imagination, challenge his attention, direct his associations, invite his contemplation, and give rise to a variety of mental emotions that may be more or less intense, and leave traces corresponding upon his physical organization. The balmy days of childhood and youth treasure the mind with ideas, whether false or true, that float down the current of time, causing happiness or misery in all the subsequent stages or conditions of life. The child acquires early in life the habit of believing in the existence and reality of things contrary to the dictates of reason and the plain truths of philosophy, and thus lays a broad and firm foundation for the fabric of duplicity and credulity that strengthens with the powers of manhood, and to which he ever after resorts to shield himself from the force and influences of truth and reason. Such are the preliminary elements of his education, that he has a peculiar relish for novelties and whatever is mysterious and inexplicable. Fearful omens absorb his contemplation by day, by which fancy threads the fearful labyrinths of the future. The zephyrs of evening his imagination converts into the whispers of demons. The fracture of a mirror or the howling of a dog are the premonitions of sickness and death; and his mental emotions may be so intense as to prove the truth of his delusions. With such preliminary elements of education of so great a number, what can be the mental acquisition and moral fruits of manhood? Let the history of ages break upon your ears in reply. Let the duplicity of the nineteenth century be regarded as its legitimate offspring. Who can measure the extent of such mental delusion, and limit its influence upon the human system in originating diseases, functional and organic? The preliminary elements of education thus briefly alluded to are conspicuous in all grades of society. They give character to the great mass of communities in all countries. Hence the speedy growth of error and credulity and superstition. Hence the dizzy heights that mark the soaring flights of quackery. Hence the remarkable cures wrought through the medium of imagination, and success that frequently inspires hope and confidence in charms and incantations. "There are more things in heaven and earth, Horatio, These expressive words of admonition were given to the world more than two hundred and fifty years ago. The unparalleled progress of science, as well as the marvelous development of art, have but established the sublime vision of its author. We may yet ascend the highest scientific pinnacle and view the unexplored fields of science, and prophetically declare the wonders which future centuries will yet bring to the devotees of scientific research and knowledge. In taking a retrospect of medical history, how cheering the thought, as we are enabled to descry in the past, men in the different decades of time who were prodigies of genius, scientific attainments, and professional skill, and who were the great centers around which revolved all the lesser lights, in whose reflection they had their scientific existence. Boerhaave's Humoralism, Cullen's Nervous Doctrine, Clutterbuck's Cerebral Doctrine, Broussais' Physi ological Doctrine, and Cook's Vena Cavaism, have each had their period of power and reign, and in their respective times have required and engrossed the professional mind so as a consequence, upon their doctrines was based the practice during the periods of their dominion. We emerged from the "sea of blood" in which the Vena Cavaism of Cook deluged us, and are now led on by the expectant and asthenic waves of the philosophy of the present time until it has found its acme in the vis medicatrix natura of Sir John Forbes, or the more absurd and radical doctrines of Hahnemann. The great minds which have illuminated the medical horizon and arose to distinction and preferment at different epochs of time, though generally either adherents of a favorite philosophy or originators of some new doctrine, were minds amply capable of the highest culture and the most extended scientific acquirements, the most accurate observations and philosophical deductions. The name of Marshall Hall has become familiar to every student and investigator of the human system throughout the world. His investigations of the anatomy of the nervous system, and his discovery of hitherto unknown and complex functions, will perpetuate his name in all time to come, and the springing up of new modes of treatment, the result of his discoveries, is daily relieving hundreds of our fellow men in every nation and country. These are the men we delight to honor, though many of their doctrines and theories live only on the page of history. They have contributed greatly to the advance of science. They merit the gratitude of the world as cultivators of science and as philanthropists. But, too great a majority of the profession are influenced and controlled by the prevailing doctrines, theories, and systems of the day, and they are too apt, I fear, to follow the established practice without investigating the scientific basis upon which such practice has been established. We are not the independent thinkers we ought to be, but more the inanimate |