ANTERIOR ABDOMINAL VEIN IN THE INDIAN TOAD. 



443 



the walls of the urinary bladder, w hich, afterall, is a possible source 

 of water. Finally, it is notewortliy that, for some reason or other, 

 Reptiles and Birds (even when aquatic) conserve their water very 

 carefully, as we may realize when we note the semi-solid character 

 of their urine*, the absence of sweat and mammary glands and 

 tlieir non-foetal rearing of offspring ; whereas Mammals, on the 

 other hand, f\re very prodigal with water in all these respects. 

 Hence it is possible that, comparatively little water being taken 

 into the gut, the liver " arranges for " an accessory supply of 

 blood in order to satisfy its water requirements. 



As to the liver, regarded as an organ of excretion in lower 

 Yertebrata, I have no evidence. 



That in the Common Frog, however (and therefore in all other 

 animals with anterior abdominal veins), the anterior abdominal 

 vein supply to the liver is not essential to the life of the animal 

 is proved by the abnormalities occasionally found t, in which the 

 anterior abdominal opens into a pre-caval instead of into a 

 hepatic-portal vein, the animal apparently being normal in all 

 other respects. 



The Ligatu7'ing of the Anterior Abdominal Vein in the 

 Common Indian Toad. 



While in India in 1915 and 1916, 1 determined to ascertain the 

 effects of ligaturing the anterior abdominal vein, though it is 

 evident that this operation will not give results comparable with 

 those to be found in the abnormalities just referred to, because 

 in the latter the blood- flow in other veins is not interfered with, 

 while in a toad with a ligatured anterior abdominal vein the 

 blood, which would otherwise flow through this, is forced to pass 

 along the two renal afferent veins — the result being increased 

 blood-pressure in the renal afferent veins and interference with 

 the renal arterial circulation J. 



In all I perfoi-med thirty-four experiments. The method I 

 finally adopted was to anaesthetize the toad with etlier, cut through 

 the belly skin and the underlying muscular body- wall for two or 

 three centimetres, ligature the anterior abdominal vein in two 

 places and remove the portion of the vein in between. Both the 

 body-wall and the skin were sewn up with sterilized silk thread 



* Sliavpe's statement (Ainer, Jouv. Physiologj% vol. xxxi.) that the water of the 

 urine of birds is absorbed in the rectum, a thick paste of uric acid remaining-, is in 

 all probability incorrect — the semi-solid urine of birds and reptiles is found in this 

 form in the ureters, and is so secreted by the kidneys. See Appendix in my paper 

 "On the ' Renal Portal' System (Renal Venous Meshwork) and Kidney PJxcretion 

 in Vertebrata," shortly to be published. 



t Woodland, W. N. F., Zool. Anzeiger, Bd. xxxv. 1910, p. 626. Also O'Donoghue, 

 C. H., ibid. Bd. xxxvii. 1911, p. 36. 



t See my paper "On the 'Renal Portal' System (Renal Venous Meshwork) and 

 Kidney Excretion in Vertebrata," Parts I. and II., shortly to be published. The 

 results of double perfusion and other experiments prove that as the pressure in the 

 renal afferent veins increases, the arterial flow becomes retarded, and above a certain 

 point is stopped altogether. Ligaturing the anterior abdominal vein in the Indian 

 toad more than doubles the amount of blood in each renal afferent vein. 



30* 



