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7. Epidemic Diarrhea a precursor of Yellow Fever
I. ENTWICKELUNGSGESCHICHTE DES HUNDE-ELES. Von Th.
L. W. Bischoff The History of the Development of the Ovum of the Dog, with
Fifteen Lithographic Plates. By Dr. T. L.W. Bischoff, Professor of Medicine, &c. in the University of Giessen. Bruns
wick, 1845. II. ZUSATZE Zur Lehre vom BAUE UND VON DEN VERRICH
TUNGEN DER GESCHLECHTSORGANE, Von Ernst Heinrich
Weber in Leipzig. Müller's Archiv. für Anatomie, 1846. Contributions to illustrate the Structure and Functions of the
Sexual Organs. By Professor E. H. Weber.
MENSCHEN UND IHREN ANTHEIL AN DER BILDUNG DER
1846. On the Glandulæ Utriculares of the Human Uterus, and on the
Share they take in the Formation of the Decidua. By Professor
Bischoff IV. DIE ENTWICKELUNG DES MENSCHEN UND DES HÜHNCHENS
im Eie, &c. Von Dr. M. P. Erdl. Leipzig, 1845-46. On the Development of the Human Embryo, and of the Chick in
the Ovum. By Professor M. P. Erdl.
The anatomy of the present day, when contrasted with that taught a quarter of a century ago, is eminently distinguished by its scientific, or, to speak more accurately, by its philosophic character; a change which has been brought about more especially by the increased attention that has of late years been devoted to those branches of organization upon which the whole subject, as a science, must eventually rest—structural anatomy, embryology, and comparative anatomy. Some have indeed questioned the advantage of the change as to any practical benefits that
NEW SERIES, NO. XI.-VI.
have been attained; but whatever regrets of this kind may in certain quarters have been expressed, they can now have no result-the new direction impressed upon the study of anatomy having become what our nearest neighbours term “ un fait accompli.”
Of the three divisions of anatomical science just named, Embryology may, in some and not unimportant points, be regarded as the most essential to the elucidation of the general laws of organization.
To those indeed whose attention has been mainly restricted to human anatomy, the history of the development of the ovum has, for the most part, been regarded only so far as of importance, as it tends to explain the formation of the various membranes of the fætus, and the relations existing between the latter and the uterus. But this inquiry has a much wider signification ; for, inasmuch as it reveals the typical forms of the several classes of organs, and their subsequent modifications and metamorphoses, such an investigation assumes a much more imposing character, and by leading the observer to discriminate between the essential and the incidental, enables him to determine the fundamental principles of animal formation. It must clearly have been the perception of this truth, joined to the general interest attaching to the production of the new being, which has excited the most distinguished physiologists of all countries, among whom it will suffice to name Harvey, Malpighi, and Hunter, to scrutinise with such persevering zeal the process of generation.
From what has been now stated, it is apparent that the study of Embryology divides itself into two branches :-one, and by far the most important and abstruse department, relates to the general laws of formation, to the essential construction of animal bodies and of their individual organs, and thus becomes, with its inseparable ally, comparative anatomy, the basis of all philosophic zoology; the second division has reference not to the development of the new being, but to the numerous and complex phenomena constituting the conditions upon which that development depends, including the various nutritive and defensive provisions by which the embryo is nourished and protected. In the present article, we shall, for the most part, confine ourselves to this latter branch of the inquiry, as being the more interesting of the two to the medical practitioner; it will, however, be proper to notice some points connected with the more comprehensive division of the subject.
It cannot have escaped the attention even of those who have considered this inquiry only in a cursory manner, that, owing to obvious causes, by far the larger portion of the information we now possess touching the constitution and development of the ovum, has been gained rather by observations made on the reproductive process of the lower animals than by any direct results that have been attained from the study of human embryology. The egg of the common fowl has been more particularly selected from the earliest periods, not less on account of its size than of the facility of making repeated examinations at successive and known epochs in the progress of its evolution. Some of the most successful inquirers of the present day, among whom we may name the justly celebrated Baer, also W. Jones, Coste, Valentin, M. Barry, and Bischoff, have, however, followed in the steps of the admirable De Graaf, of whom a distinguished physiologist justly remarks, that he " has made a series of 1847]
Component Parts of the Ovum.
researches upon the first consequences of conception, which have been equalled by few of his successors and surpassed by none.
."* They have thus obtained many accurate details from the patient examination of the minute mammiferous orum; nay, even some of the best examples of the earlier changes in the egg consequent upon impregnation, have been derived from the investigation of other diminutive ova, as those of the acalephæ by Siebold, of the entozoa by Bagge, and of insects by Kölliker.
So large a part of our present knowledge thus resting on comparative embryology, and as in the human being all accurate investigation is opposed by so many obstacles, some of which are insuperable, it becomes a point of the firet importance to know how far the deductions drawn from the study of the lower animals, can be applied to man. The only mode in which this prime question can be solved, is by considering, in the first place, what are the component parts of the egg in the different classes of the animal kingdom; and, in the second place, what are the changes consequent upon the fertilization of the ovum. In the prosecution of these inquiries, it will be necessary to enter into details at the hazard of stating facts that are perhaps familiar to some of our readers, but which, notwithstanding their important bearing upon the whole question, have not, in our estimation, received the attention they demand. These preliminary inquiries will, at the same time, form the most natural introduction to the important work of Professor Bischoff, to which we design more particularly to direct the attention of our readers.
Touching the essential parts of the ovum, there is no doubt of their universal existence in all animals. By these parts are meant the germinal vesicle together with its macula, and the yelk with its membrane ; these are met with equally in the vertebrata and invertebrata, in the smallest as in the largest eggs. The constant presence of these parts points to their supreme importance; and the progress of modern science, although it leaves the question of the first origin of the embryo in its original obscurity, still enables us to interpret the respective shares which the parts just named take in the subsequent development of the germ. The germinal vesicle, first discovered in 1825 by Purkinje in the cicatricula of the hen's egg, and subsequently and independently by Wharton Jones, Coste, and Valentin, in the ovum of mammals, is, with its contained germinal spot (discovered by Rudolph Wagner), that part of the egg which subsequently, by a process not even yet thoroughly known, becomes transformed into the rudiments of the germ. As to the yelk or vitellus, it takes no direct part either in the primitive formation or in the subsequent growth of the embryo; but it is essential inasmuch as it furnishes, either wholly or for a time, the nutritious matter required for the support and development of the new being.
In the case of all oviparous animals, this relation of the vitellus to the nourishment of the embryo, is immediately apparent; and it will subsequently appear that many important acts of development, which take place in mammals as the ovum traverses the Fallopian tube, and even for a part of the time, whilst it is still unattached in the uterus, are effected at the
* Handbuch der Entwickelungsgeschichte, von Dr. G. Valentin, p. 32.