420 CONDITIONS FAVOURING TRANSLATION. 



greater transudation of fluid through the blood-vessels. The abdominal blood- 

 vessels, and those which yield a watery effusion under normal circumstances, are 

 those most liable to be affected. 



Transudation is favoured by (1) Venous congestion, in which case the effusion 

 usually contains little albumin, and few lymph-corpuscles, while the coloured-cor- 

 puscles on the contrary are more numerous the greater the venous obstruction. 

 Ranvier produced oedema artificially by ligaturing the vena cava in a dog, and at the 

 same time dividing the sciatic nerve. The paralytic dilatation of the blood-vessels 

 thereby produced caused an increased amount of blood to pass to the limb, while the 

 blood-pressure was raised, and both factors favoured the transudation of fluid. 

 [Ranvier's experiment proves that mere ligature of the venous trunk of a limb by 

 itselfis not sufficient to cause oedema. The oedema is due to the concomitant paralysis 

 of the vaso-motor nerves. If the motor roots of the sciatic nerve alone be divided 

 along with ligature of the vena cava, no oedema occurs, but if the vaso-motor fibres 

 are divided at the same time, the limb rapidly becomes oedematous. There is such an 

 increased transudation through the vascular walls that the veins and lymphatics 

 cannot remove it with sufficient rapidity, and oedema occurs. If there be weak- 

 ness of the vaso-motor nerves, slight obstruction is sufficient to produce oedema 

 (Lauder Brunton).] When the leg veins are occluded with an injection of gypsum, 

 oedema occurs (Sotnischewsky). (2) Some unknown physical changes occur in 

 the protoplasm of the endothelium of the capillaries and blood-vessels, which 

 favour the transudation of albumin, haemoglobin, and even blood-corpuscles. 

 This occurs when abnormal substances accumulate in the blood e.g., dissolved 

 haemoglobin and when the blood contains little or albumin. The same has 

 been observed after exposure to too high temperatures, and the swelling of 

 soft parts in the neighbourhood of an inflammatory focus seems due to the 

 transudation of fluid through the altered vascular wall. It is probable that a 

 nervous influence may affect particular areas, through its action on the blood- 

 vessels of the part (it may be upon the protoplasm of the blood-capillaries). 

 The transudations of this nature usually contain much albumin and many lymph- 

 corpuscles. (3) When the blood contains a very large amount of water the 

 tendency to transudation of fluid is increased. After a time it may produce the 

 changes indicated in (2), and when long continued may increase the permea- 

 bility of the vascular wall (Cohnheim). Watery lymphatic effusions from watery- 

 blood " cachectic oedema," occur in feeble and badly nourished individuals. 

 [One of the commonest forms of dropsy is the slight oedema of the legs in 

 anaemic persons, in whom the heart and lungs are healthy. Many factors are 

 involved the watery condition of the blood, the condition of nutrition of the 

 capillaries, and probably a tendency to vaso-motor paresis (Brunton).] 



[ (4) Ostroumoff found that stimulation of the lingual nerve not only causes the 

 blood-vessels of the tongue to dilate, but the corresponding side of the tongue 

 becomes oedematous. If a solution of dilute hydrochloric acid or quinine (p. 287) 

 be injected into the duct of the submaxillary gland, and the chorda tympani 

 stimulated, there is no secretion of saliva, but the gland becomes oedematous. In 

 an animal poisoned with atropin, stimulation of the chorda causes dilatation of the 

 blood-vessels, although there is no secretion of saliva, nevertheless the gland does 

 not become cedematous (Heidenhain). As Brunton suggests, this experiment 

 points to some action of atropin on the blood-vessels which has hitherto been 

 entirely overlooked.] 



204. Comparative Physiology. 



In the frog, large lymph-sacs, lined with endothelium, exist under the skin, 

 While large lymph-sacs lie in relation with the vertebral column one on each side 



