TENTH LECTURE. 



THE LYMPHATICS AND THE LYMPHATIC GLANDS. 



WHAT is understood by lymph we have already mentioned 

 in our second lecture (p. 27). It was the blood plasma which 

 had passed out through the capillary walls, and which gave 

 off the dissolved nutritive constituents to the tissues, and took 

 up in exchange the products of the decomposition of the lat- 

 ter. We even then mentioned that this fluid, which is unin • 

 terruptedly supplied from the blood current, must necessarily 

 be removed. The arrangement serving this purpose must 

 now be discussed. 



Our present course will, however, be the reverse of that 

 followed in the previous lecture ; for the large and medium 

 lymphatic discharge tubes are more accurately known, while 

 numerous uncertainties still prevail concerning the knowledge 

 of the finer and finest elements. 



Let us commence with the ductus thoracicus, the terminal 

 large discharge tube of the lymphatics. We here meet with 

 a condition corresponding to the walls of the veins. 



The endothelium is surrounded as a serosa by several layers 

 of a striated substance, and then by a net-work of longitudi- 

 nal elastic fibres. As a middle layer, we have next, longitu- 

 dinally running connective tissue, and then transverse mus- 

 cles. The adventitia also shows remains of the latter tissue. 

 Valves are not wanting here, nor afterwards in the finer 

 lymphatics. 



Descending to the latter, the stratification, as in the veins, 

 becomes more simple ; but more accurate studies are here 

 still necessary. In small trunks of 0.2 to 0.3 mm., the four 

 characteristic vascular layers have been found still present. 



The adventitia, media and serosa gradually disappear, and 



