12 ANATOMY OF THE LYMPHATIC SYSTEM. 



that in full-grown animals there exist only tracts and large patches, 

 as there exist also here, as has been already mentioned, smaller patches 

 situated laterally to the tracts. It may be deduced from this that 

 in the omentum there is going on a continuous growth and new- 

 growth of opaque patches, which, by growing in length and coalescing 

 in the direction of their longitudinal axis, form tracts. 



A portion of the fresh omentum is a very unfit object for the 

 study of the cellular elements of the ground-substance : besides the 

 above-mentioned germinating endothelium, only more or less nu- 

 merous migratory cells can be seen on and in the patches and tracts. 

 There is only one mode of preparing that gave me good results, that 

 is, the mode of staining the fresh omentum with silver solution after 

 having pencilled it gently on one surface. I proceed in the following 

 way : a rabbit is killed by bleeding, the stomach is exposed ; after 

 having pushed the intestine to the right side, the free surface of the 

 omentum is pencilled several times, from the large curvature towards 

 the diaphragm, with a fine camel's hair pencil moistened with fluid of 

 the abdominal cavity. After that, a quarter or half per cent, solution 

 of nitrate of silver is allowed to flow over the omentum from a large 

 capillary tube, until the membrane has become slightly milky (one 

 to two minutes are generally sufficient) ;" after that, the stomach, 

 together with the omentum, spleen, pancreas, and a portion of the 

 duodenum is cut out and transferred to a large capsule with distilled 

 water ; after some time the water is renewed, and the omentum is 

 separated under water, together with the spleen and pancreas, from 

 the stomach with scissors and is transferred to common water. Those 

 portions of the omentum which are seen to contain small patches are 

 cut out and mounted, as has been already described. A failure is 

 more frequent than a success : either the surface has not been pencilled 

 enough, and then the endothelium of both the surfaces is coloured, 

 and consequently, hardly anything is to be seen of the cellular ele- 

 ments of the ground-substance ; or the surface has been pencilled too 

 hard, and then the arrangement of the ground-substance is altered, 

 its bundles appear considerably stretched and distinctly fibrillar. 

 Successful preparations become only slightly yellowish brown, and 

 can be preserved without alteration for a very long time. 



