Paper - General observations on early superficial lymphatics in living chick embryos (1912)

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Clark EL. General observations on early superficial lymphatics in living chick embryos. (1912) Anat. Rec. 6: 249-254.

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This historic 1912 paper by Clark describes the early superficial lymphatics in living chick embryos.

Modern Notes: lymphatic | chicken

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General observations on early superficial lymphatics in living chick embryos

Preliminary Note

Eleanor Linton Clark From the Anatomical Department of The Johns Hopkins University

Last fall an attempt was made to study the development of the superficial lymphatics of the chick by injections with India ink. In chicks of seven days and over it was very easy to study the character and extent of the lymphatics by this method, but in younger embryos I found it increasingly difficult to obtain satisfactory lymphatic injections, since in almost every case the superficial blood capillaries were injected at the same time. However, it was occasionally possible to inject an irregular plexus over the pelvis, and from it a deeper plexus connected with the intersegmental coccygeal veins, in the exact region occupied by the functioning posterior lymph heart of older embryos.

A living chick of five days and twenty hours was then examined under the high power binocular microscope, in bright sunlight. Care was taken in opening the shell not to injure the embryo, and the j^olk sac was kept intact. Observation of the region in the tail, later occupied by the posterior lymph heart, revealed the presence of two distinct sets of vessels. The first of these was undoubtedly composed of blood capillaries. With brilliant illumination this richly anastamosing plexus could be plainly seen and the direction of circulation in the individual capillaries made out.

But in the living chick another distinct blood-filled plexus was visible. For the most part it appeared to be deeper than the superficial blood capillary plexus and nearer the coccygeal veins. This second plexus was found to be easily distinguishable from the blood capillaries in four ways: (1) the vessels composing it are in general larger than the blood capillaries, (2) their pattern is different, (3) the blood contained in them is of a darker red color, and (4) no circulation can be observed in them. The last feature is the most striking, for in contrast to the rapid motion of the blood corpuscles in all of the capillaries of the first plexus, the blood of this second plexus remains stagnant. This plexus of vessels with stagnant blood was found to be constant in chicks of this and somewhat later stages.

Next, various tests were made to determine further the character of this plexus filled with stagnant blood, and its relation to the blood vascular system. They are as follows:

1. In a living chick a few granules of ink were injected into several of the circulating blood capillaries. The granules were seen to pass through the capillaries and venules into the main intersegmental veins, but in no case did they enter this stagnant plexus.

2. The plexus filled with stagnant blood was injected. After the discovery that at this early stage the lymphatics could be distinguished from the blood vessels in the living chick, much of the difficulty of the former injections could be avoided. A very small glass canula is used (from 12 to 15 micra in diameter at the tip) and with the aid of the high power binocular microscope, it is not difficult to insert the needle directly into a selected Ij^mphatic capillary. Since these vessels are filled with blood, it is easy to overdistend them, but if a gentle pressure is used it is possible to obtain injections with no extravasation. When this method was substituted for the former one of plunging the needle blindly into the tissue, the neighboring blood capillaries were never injected simultaneouslj^ with the lymphatics. In all cases they remained undisturbed.

Wherever the injection of the lymphatics is pushed far enough the ink runs back from the surface vessels, into the deeper plexus, and from it into the five intersegmental coccygeal veins. At no other point does the ink ever enter the venous system from a direct injection of this early posterior plexus filled with stagnant blood.

3. The superficial blood capillaries of this region were then injected. In no case did tlio ink enter the stagnant plexus, which still roinaiiKMl hUccl with blood and (|iiit(' iii<l<'p<'ii<l(Mit of the injected blood capillaries:

4. Coinplcte blood vascular injections were obtained throufih one of the larfiic vessels of the yolk sac or allantois. Here too the blood-filled lymphatic plexus remained uninjected with ink.

5. Double injections were also obtained. In one six-day chick, I injected the blood-filled lymph heart plexus with ink, stopping the injection just as it entered the coccygeal veins. The surface blood cai)illaries were then filled with Berlin blue. On the other (left) side of the same specimen, the superficial blood capillaries were first filled with the Berlin blue, leaving the blood in the lymph heart plexus. The main sub-cardinal vein was then injected with India ink. Its branches, the coccygeal veins, soon filled and, since the Berhn blue previously injected blocked ofT the blood capillary branches, the ink, was forced into the blood-filled lymphatic plexus. In both cases the injections showed strikingly the lymphatic connections with the intersegmental veins and showed conclusively that there is no other communication with the blood vascular system in this posterior region.

6. Injections of the blood-filled lymphatics with silver nitrate were also obtained which showed that these early vessels possess definite endothelial markings.

7. When the large arteries and veins of the yolk sac and allantois were opened and the embryo was allowed to bleed freely, the blood could be seen to fade out of the superficial blood capillaries in which the circulation had previously been observed. However the blood did not fade from the lymphatic plexus, which remained undisturbed by the bleeding and still filled with the dark 1-ed stagnant blood.

To summarize the results of these observations:

Early lymphatics can be seen in the living chick and can be distinguished from the blood capillaries of the same region by several criteria, the most noticeable of which is that they are filled wdth stagnant blood.

In and near the region later occupied by the posterior lymph heart these blood-filled lymphatics are seen to form a plexus whose connections with five of the intersegmental coccygeal vein can readily be demonstrated by injection.

Various injection tests also show that this early lymphatic plexus is independent of the surrounding blood capillaries, for each of the two sets of vessels can be injected separately without disturbing the other.

The fact that the blood contained in this early plexus is stagnant — that is, backs up into it from the vein — shows that the early lymphatics pass through a distinct non-functioning stage.

In studying the development of the jugular lymph sac, F. T. Lewis, and later other investigators, have shown the presence of a capillary plexus preceding the formation of a definite sac. In most cases they have pictured this plexus as a group of isolated channels and vessels known as veno-lymphatics and have interpreted them as a transformed blood-capillary plexus. It has been inferred that this stage was preceded by one in which the vessels, which later are going to form lymphatics, are an integral functioning portion of the blood vascular system. In an article in this number of The Record on injection and reconstruction of the jugular lymph sac, I have shown that the appearance of isolation of parts of this early plexus, shown in reconstruction, is attributable to the limitations of the method. In the case of the posterior lymph heart, observation of the living chick shows that the early plexus is not composed of isolated vessels but is a definite continuous plexus connected with the intersegmental coccygeal veins. And the fact that the plexus is filled with stagnant blood and is therefore non-functioning, together with the fact of its being entirely separate from the surrounding blood capillaries, prevent me from regarding it as a true blood-vessel plexus. It is therefore proper to consider this plexus of vessels filled with stagnant blood as a non-functioning lymphatic plexus.

Having established the fact that the early lymphatics are filled with stagnant blood and can therefore be seen in living chick embryos, we have an entirely new method for the study of their development. In an accompanying article is given a preliminaryreport of the results of such a study of the very earliest lymphatics. In a later article will be published the results of studies on later stages. In brief, it has been found that a non-functioning plexus, packed with blood and similar to the posterior lymphatic plexus, develops in the lower cervical region and under the sJiDulder in connection with the anterior and posterior cardinal veins near their junction to form the duct of Cuvier. The nonfunctioning period, during which the lymphatics are filled with blood, lasts for from twenty-four to thirty hours. During this time a rapid extension of the two plexuses takes place which may be observed in living embryos.

Cite this page: Hill, M.A. (2021, April 14) Embryology Paper - General observations on early superficial lymphatics in living chick embryos (1912). Retrieved from

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