The Origin and Development of the Lymphatic System. 15 



and erroneous conclusion that the empty vessels, though they might 

 have some of the functions of the lymphatics of the adult, could not 

 properly be grouped with them. We now know that the two sorts of 

 empty vessels are (1) the collapsed blood vessels which Mayer himself 

 observed and (2) the true lymphatics (B. R. Clark, 26). 



The work of Mayer, however, has another point of great interest 

 to us beside the important observation of the contractility of endo- 

 thelium, namely, what we call Mayer-Lewis anlagen. Mayer noted 

 the long strands of cells (endothelium) which often span the gap 

 between two capillaries; indeed, he figures them, some that look 

 entirely solid and some that have, here and there, a patent lumen. In 

 reality both blood capillaries and lypmhatic capillaries have these 

 strands and sprouts, and it is one of the most remarkable qualities 

 of the two forms of endothelium that no sprout from a lymphatic 

 capillary ever joins a blood capillary and vice versa. However, Mayer's 

 mistaken idea that these strands of cells connected with two different 

 kinds of capillaries, namely, the vessels which are always empty, in 

 other words, the lymphatics and the blood capillaries, aided in his 

 confusion of the lymphatics with the blood vessels. Besides these 

 strands of endothelium he saw small hollow vessels, having the same 

 lining as the capillaries, which he thought to be entirely isolated. 

 These he interpreted as follows (p. 236) : 



Unseren Erfahrungen nach sind nun die beschriebenen Bilder nur gewisse 

 Stadien der Ausschaltung von Bestandtheilen des Blutgefassystems aus der 



normalen Circulation Bei genauerem Studium der letzteren For- 



mationen ergibt sich, dass die Wandungen derartiger mit freien Spitzen in 

 das Gewebe hineinragenden, und ausserhalb jeder Kommunication mit 

 Gefassrohren stehenden Fragmente beziiglich des Aufbaues ihrer Wand 

 entweder mehr den- Typus der blutleeren oder demjenigen der blutbaltigen 

 Rohrchen sich nahern. 



Most of the apparently isolated anlagen seen in sections are due 

 to the collapsing of the vessels which connect them with the rest of 

 the capillaries through the contractility of the endothelium which 

 Strieker and Mayer observed. In sections they may occur in great 

 numbers through the contraction of the endothelium due to the fixing 

 agent. The possibility of entirely isolated vessels and the meaning 

 of the apparently isolated vessels are fully discussed later in connec- 

 tion with the theory of the growth of lymphatic capillaries by the 

 addition of Mayer-Lewis anlagen in section VIII. 



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