INJECTION AND RECONSTRUCTION OF THE JUGTJLAR LYMPH “SAC” I N THE CHICK ELEANOR LINTON CLARK From the Anatomical Laboratory of T h e Johns H o p k i n s University T W O FIGURES It has recently been pointed out that the present difference of opinion in regard to the mode of development of the lymphatic system is due largely to the method employed in studying the subject. Those authors who have used exclusively the method of reconstruction from cross sections, have represented the earliest lymphatics as isolated channels and spaces. From this two theories have arisen: 1. The view tentatively advanced by F. T. Lewis that the development is by the addition of portions of blood capillaries which have been cut off from the general blood vascular system; and 2. The theory championed vigorously by Huntington, McClure and others, that the extension of lymphatics is by the transformation and addition of isolated spaces in the mesenchyme. On the other hand, the theory of centrifugal growth has been brought forward by Ranvier, Sabin, MacCallum and Hoyer, who used the method of injection as well as the study of cross sections, and by Clark who based his work on observations of living lymphatics. These authors picture the early lymphatics as continuous and state that their extension is accomplished by sprouting of the endothelium. The limitation of the reconstruction method has been amply tested by Clark who made careful drawings of living lymphatics in the tadpole’s tail and subsequently attempted to reconstruct these same vessels. Similar tests were made by Sabin on the embryo pig, to compare the method of reconstruction with that 261 262 ELEANOR LINTON CLARK of injection. These studies made it clear that the lymphatics cannot be completely reconstructed, for vessels which in the living embryos and in injected specimens are seen to be continuous, appear in cross sections as isolated spaces. This accounts for the discrepancies in the chief views concerning the development of lymphatics. The recent publication by A. M. Miller‘ in The American Journal of Anatomy has given me the opportunity to compare the value of the two methods in studying the development of the jugular lymph sac in the chick, since I have succeeded in making numerous injections of the same region and stages which Miller has reconstructed. These injections show that in chicks between five and one-half and seven days the developing lymph ‘sac’ which appears in Miller’s reconstructions as a scattered group of isolated ‘islands and channels,’ is in reality a dense and continuous lymphatic plexus. The accompanying drawing, fig. 2, was made from an injected specimen of the jugular lymphatic plexus in a chick of the same size and stage as fig. 1 (reprinted from fig. 3 in Miller’s paper), judging by the measurement and by the appearance of the neighboring veins. A comparison 6f the two demonstrates again that much of the early lymphatic system cannot be seen in cross section and therefore cannot be reconstructed. Students of chick embryology have always encountered difficulties in determiningwith accuracy the various stages, on account of the evident variations in the degree of development of two embryos of the same age or measurement. From Miller’s descriptions it is not possible to determine the exact stages presented in his figures. Therefore in case my figure may not represent exactly the same stage as Miller’s fig. 3, it may also be compared with his fig. 1, which shows a chick of the same age as my specimen, or with his fig. 4 which shows a reconstruction of an older embryo. I n any case the contrast between the continuous plexus disclosed by injection and the isolated islands shown by reconstruction is most striking. ‘A. M. Miller, “ T h e Development of the Jugular Lymph Sac in Birds,” ;\merican Journal of Anatomy, Vol. 12, No. 4, p. 473, Jan. 1912. INJECTION AND RECONSTRUCTION 263 Fig. 2 . Lateral view of jugular lymphatic plexus of the right side in a chick embryo incubated five days and twenty hours, measuring 14 mm., greatest length, after fixation. By means of a very fine glass canula (about 15 micra i n diameter a t t h e tip) dilute India ink was injected, under the binocular mircoscope, directly into one of the superficial lymphatics of the body wall, between the arm and leg. From here the ink filled the deep jugular lymph plexus and from i t a few granules entered the vein through five connections ( C ) . The drawing was made with the assistance of a camera lucida with a Zeiss binocular, oculars no. 4, objectives As. Enlarged 50 diameters. A , vessel connecting the superficial lymphatics, into which the injections were made, with the jugular lymphatic plexus; A.C., anterior cardinal vein; P. C., posterior cardinal vein; D. C., duct of Cuvier; C., communications between jugular lymphatic plexus and vein; D.,deep lymphatic, T.E . V., thoraco epigastric vein; C . L. D.,cervical lymphatic duct. Compare with Fig 1, which is a reprint of Miller’s diagram drawn from a reconstruction of this region in a chick of approximately t h e same stage. 264 ELEANOR LINTON CLARK I have also made injections in chicks of seven days,-the stage shown in fig. 6 of Miller’s paper. Here instead of the ‘sac’ described by Miller, the injected specimens show that an extensive plexus is still present. The vessels composing it are larger than in the younger chicks, and Miller has probably figured the largest of these, which in my injections is seen to be continuous with a large lymphatic duct lying next the jugular vein and extending the whole length of the neck. No doubt this is Miller’s lymph ‘sac’ of the seven-day chick. I have not yet studied this region in chicks older than eight days, but the injections of chicks between seven and eight days confirm Mierzejewski in his descriptions of a ‘lymphatic plexus’ in contrast to the ‘sac’ figured by Miller. I may add that in all the chicks injected between five and onehalf and eight days I was able to demonstrate a connection with the venous system. I n the younger chicks (see figure) the connections are more numerous, but subsequently the number is reduced to one or two. I should therefore seriously question Miller’s statements in regard to the separation of the sac from the vein and its subsequent reunion with it. I do not claim that any of my injections, including that, shown in the figure, are entirely complete but, as far as they go, they are positive. They reveal the presence of a definite continuous lymphatic plexus in a region where only isolated spaces can be demonstrated by the reconstruction method.