CHAP. XXVI.] ORIGIN OF THE LYMPHATICS. 277 



animals and in man, than those comparatively large ones which 

 compose the plexuses just mentioned. Kolliker observed these 

 vessels during life, and satisfied himself of their continuity with the 

 neighbouring lymphatic trunks. He found them about the same 

 size, but less numerous than the blood-capillaries, and composed of a 

 simple, very delicate membranous wall, projecting into small pointed 

 processes, here and there, and containing a few flattened nuclei. 

 The pointed processes may belong only to their rudimentary, and 

 not to their completely developed condition. He states that they 

 ramify in an arborescent manner, without anastomosing, and end by 

 free closed extremities. They have no valves, and remain of the 

 same width during life, but after death, exhibit the same contrac- 

 tility, though not of so active a kind, as the capillaries, by lessening 

 uniformly in diameter during a certain time. He was able to 

 detect the movement of their transparent contents by that of the 

 granules and lymph-corpuscles which, in rare instances, they were 

 observed to contain, and found it to be continuous, and very slow, 

 almost twelve times as slow as that of the blood in the capillaries. 

 He found the mode of development of these primary lymphatics to 

 resemble closely that of the capillaries, i.e., it takes place by the 

 outgrowth and subsequent coalescence and tubulation of processes 

 from contiguous nucleated cells. 



Kolliker's observations on the relations of these minute lym- 

 phatics with the capillaries are interesting. He found that when 

 the current of blood was regular, there was no appearance of com- 

 munication between the two orders of vessels, but that when the 

 circulation was excited and tumultuous, owing to the confinement 

 of the tadpole under glass, during the observation under a high 

 magnifying power, red blood-corpuscles escaped more or less readily 

 from the blood-vessels into the contiguous lymphatics; and in 

 several instances he was able to detect actual communications 

 between lymphatics of the finest kind and the network of capillary 

 blood-vessels. After careful inquiry, however, he concludes that 

 these junctions are due to rupture, or, perhaps, in some cases, to 

 a primitive abnormal formation. He further noticed a reflux of 

 blood into the lymphatics through the orifices by which their 

 trunks open into the larger veins. This retrograde current was 

 almost always observed when the respiration was impeded by 

 want of water, and the veins were consequently gorged, or when 

 a ligature was placed round the head. In the latter case, the 

 whole lymphatic tree was often fully and beautifully injected with 

 blood. 



