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SCIENCE 



[N. S. Vol. XLIV. No. 1127 



the other hand, it is known that granules 

 are in large part taken up by special large 

 phagocytic cells, some of which pass into the 

 lymphatics of the diaphragm. This gives 

 a suggestion of a possible differentiation in 

 absorption between blood-vessels and lym- 

 phatics. Indeed, a partial differentiation in 

 function is a most familiar phenomenon : I 

 refer to the villi of the intestine, where al- 

 most all of the fat passes into the central 

 lacteal while the carbohydrates pass di- 

 rectly into the blood-stream. It is well 

 known, on the other hand, that when a 

 needle is introduced into certain areas 

 under the skin or into specific layers of 

 many of the organs and a fluid containing 

 granules is injected, the granules always 

 appear in the lymphatic trunks which drain 

 the area. What is the difference between 

 tissue-spaces which are drained by lym- 

 phatics and those which are not? What is 

 the difference between areas in which in- 

 jections always show lymphatics and those 

 which never show lymphatics? What is 

 the nature of the fluids which pass through 

 the lymphatics and those which do not? 

 In other words, exactly what happens at 

 the point of the needle when an artificial 

 edema is produced? This I understand to 

 be the meaning of the main problem con- 

 nected with the lymphatic system — the so- 

 lution of the enigma of the mechanism of 

 absorption. The difficulty of the problem 

 was well expressed by Bartels 6 as late as 

 1909, when he said that the relation of the 

 lymphatic capillary to the tissue-spaces was 

 a philosophical rather than an anatomical 

 problem. My understanding of the recent 

 work on the lymphatic system is that it 

 tends to take the system out of the realm 

 of the mythical and to make it a definite 

 anatomical entity. The investigations of 

 the last fifteen years have demonstrated 

 6 Bartels, P., ' ' Das Lymphgef Sssystem. Hand- 

 buch der Anatomie des Menschen," Von Barde- 

 leben, 1909. 



that the blood-vessels are the primary ab- 

 sorbents, and that subsequently partial sys- 

 tems of absorbents develop, such as the 

 arachnoidal villi and the lymphatics which 

 drain into the veins. 



I have been greatly interested in the at- 

 tempts of the earlier anatomists to solve 

 the problem of absorption. They brought 

 to the subject of tissue-spaces and the fluid 

 within them a great freshness of interest 

 and constantly sought to understand the 

 meaning of their various observations. 

 They saw the arteries become smaller and 

 smaller, they were familiar with lymphatic 

 trunks and with some lymphatic capillaries. 

 What then was more natural than to as- 

 sume that when the arterioles became so 

 small that the corpuscles could not enter, 

 there were still smaller vessels which car- 

 ried the plasma over into the lymphatics? 

 These tiny hypothetical vessels were called 

 "vasa serosa." A belief in their existence 

 was held throughout the eighteenth cen- 

 tury, and was not overthrown until the dis- 

 covery of cells by Schwann in 1830. 

 Schwann believed that the mesenchymal 

 cells were hollow and from this idea 

 Virchow formulated the theory that hollow 

 connective-tissue cells spanned the gap be- 

 tween the blood-vessels and the lymphatics. 

 Then followed the discovery by von Reck- 

 linghausen that the wall of the lymphatic 

 capillary was composed of cells. Von 

 Recklinghausen thought that silver impreg- 

 nations showed that lymphatics spread out 

 as lymph radicles or lymph rootlets into the 

 tissue-spaces. At first His believed in these 

 lymph radicles, that is, in open lymphatics, 

 but von Recklinghausen's discovery of 

 endothelium led him to a conception of a 

 lymphatic capillary as a definite, closed 

 vessel, this conception being confirmed by 

 his own experience with injections. If 

 lymphatics open out into tissue spaces every 

 injection of a capillary plexus with a non- 



