$32 PHILOSOPHY OF ZOOLOGY. 
found pale and inert. These facts seem to warrant the 
conclusion, that the spleen is subservient to the functions of 
the liver, and probably supplies the deficiency of fluid which 
the branches of the vena portarum are unable to obtain 
from the abdominal viscera. 
Sir Everarp Home at one time considered the spleen as 
the medium by which fluids, unnecessary for the process of 
digestion, were conveyed from the cardiac portion of the 
stomach, into the system, or into the urine to be excreted. 
But, in subsequent experiments which he performed, co- 
loured fluids mjected into the stomach, reached the urine, 
even when the spleen had been previously extirpated, and 
even after a ligature prevented the contents of the thoracic 
duct from being poured into the circulating system. Al- 
though he adopted this opinion hastily, with a praiseworthy 
candour he frankly published the demonstration of his er- 
ror *. 
I have said hastily, because the well known circum- 
stances of quadrupeds which do not drink, possessing a 
spleen equal in size to those which swallow large quantities 
of fluid, and the attachment of this organ to the first sto- 
mach of ruminating quadrupeds, into which the drink does 
not enter, furnished objections of great weight. 
The next organ in connection with the digestive system, 
is the Peritoneum. This membrane lines the walls of the 
abdomen, and insinuates itself among the intestines, form- 
ing various duplicatures, distinguished by appropriate 
names. It is composed of cellular tissue, and contains nu- 
merous bloodvessels and absorbents. Its free surface is 
kept constantly moist by an aqueous exhalation. It varies 
in thickness and tenacity in different animals ; and although 
transparent or whitish among quadrupeds and birds, is found 
variously coloured in reptiles and fishes. Its obvious use 
is to protect the intestines from rubbing against one an- 

* Home’s Lect. on Comp. Anat, vol. i. p. 221,—245. 
