COMPARATIVE. 



375 



time due to the fact that a copious transudate is furnished on the part of the blood- 

 vessels. Obstruction in the distribution of the lymph-stream may then further 

 increase such a collection of fluid. Particularly the vessels of the abdomen and, 

 further, those that furnish a watery exudation also under normal circumstances 

 appear, above all others, to be especially adapted to transudation. Such increase 

 in transudation is favored by (i) any considerable degree of venous stasis. These 

 hypostatic transudates are, as a rule, deficient in albumin and leukocytes, but, 

 on the other hand, the richer in erythrocytes the greater the interference with the 

 flow of venous blood. Ranvier induced hypostatic edema artificially in the 

 lower extremity by ligation of the inferior vena cava and simultaneous division 

 of the sciatic nerve. The paralytic dilatation of the vessels of the posterior 

 extremity, induced by the latter, causes an increase in the amount of blood present 

 and a rise in the blood-pressure, which, in turn, promotes edematous exudation. 

 (2) Further, as yet unknown physical changes in the protoplasm of the endothelial 

 cells of the blood-vessels and capillaries may render these capable of permitting 

 the abnormal passage of albumin, hemoglobin and even blood-cells. This takes 

 place when foreign matters are present in the blood in considerable amount, 

 as, for example, hemoglobin in solution; further, when the blood is deficient in 

 oxygen or albumin. Also after exposure to abnormal heat, a similar condition 

 has been observed, and the tumefaction of the soft parts in the vicinity of inflamed 

 tissues likewise appears to be due to an exudation of lymph through altered 

 vessel-walls. Perhaps a nervous influence, which makes itself felt in a certain 

 vascular area (by contraction or relaxation of the protoplasm of the blood-capil- 

 laries ?) , may even be capable of causing such a transitory change in the vessel- 

 walls. Lymphatic transudates of this character are generally rich in cells and 

 consequently also in albumin. (3) Further, the presence of a large amount of 

 water in the blood will increase its capacity for transudation. Nevertheless, 

 the fact should be considered in this connection that the large amount of water 

 contained in the blood acts, in turn, by inducing changes in the protoplasm of 

 the endothelium of the blood-vessels and capillaries, so that it is itself, when 

 long continued, a factor that increases the permeability of the vessel-walls. 

 Debilitated, poorly nourished, flabby individuals particularly exhibit watery 

 lymphatic exudations from watery blood cachectic edema. 



There is no doubt that lymph-stasis (hydrops) may develop also under cer- 

 tain circumstances, and even through the action of microorganisms (bacterium 

 lymphagoguni) , in consequence of the fact that irritation of the cells of the blood- 

 capillaries (as by the products of metabolism of that organism) gives rise to 

 increased exudation of fluid. 



COMPARATIVE. 



Extensive lymph-spaces, lined with endothelium, are present in the frog, 

 beneath the entire external integument. In addition, a large lymphatic space, the 

 cysterna lymphatic magna of Panizza, extends in front of the vertebral column, 

 separated from the abdominal cavity by the peritoneum. Tailed amphibia, 

 as well as many reptiles, have large lymph-spaces beneath the skin, occupying 

 the entire length of the trunk in the lateral regions of the back. Further, all 

 reptiles and the tailed amphibia possess, in the course of the aorta, large, longi- 

 tudinal lymph-reservoirs. Tortoises likewise have an extensive lymphatic ap- 

 paratus (Fig. 130, A, II). The bony fish have longitudinal lymph-trunks 

 in the lateral regions of the back, from the tail to the anterior fins, and these are 

 connected with dilated lymph-spaces at the root of the tail and the fins of the 

 extremities. Within the interior of the body the extensive lymph-sinuses attain 

 their greatest development in the region of the gullet. Many birds possess a 

 sinus-like dilatation of a lymph-space in the region of the tail. In the carnivora 

 the mesenteric lymph-glands are united to form a large, compact mass, the so- 

 called pancreas of Aselli. Naturally the lymph-spaces (provided with valves) 

 always communicate with the venous system, and usually with the territory 

 of the superior vena cava. 



HISTORICAL. 



Although the lymph-glands were known to the school of Hippocrates, espe- 

 cially through their morbid enlargement, and although Herophilus and Erasistratus 

 had observed the milk-white chyle-vessels in the mesentery, Aselli (1623) was the 



