PARTS OF ANLMALS, III. vii. 



have blood in them and so are hot. The kidneys 

 assist in connexion with the residue which is excreted 

 into the bladder. 



Now the heart and the liver are necessary to all 

 animals. The heart is necessary because there must 

 be a source of heat : there must be, as it were, a 

 hearth, where that which kindles the whole organism 

 shall reside ; and this part must be well guarded, 

 being as it were the citadel of the body. The liver is 

 necessary for the sake of effecting concoction. All 

 blooded creatures must have these two viscera, and 

 that is why these two are always present in them. 

 A third, the lung, is present in those animals that 

 breathe. 



But the spleen, where present, is present of necessity spleen. 

 in the sense of being an incidental concomitant, as 

 are the residues in the stomach and in the bladder. 

 So in some animals the spleen is deficient in size, 

 as in certain birds which have a hot stomach, e.g. 

 the pigeon, the hawk, and the kite ; the same applies 

 to the oviparous quadrupeds (all of these have an 

 extremely small spleen) and to many of the scaly 

 creatures. These animals just mentioned also lack 

 a bladder, because their flesh is porous enough to 

 enable the residues formed to pass through it and , 

 produce feathers and scales. For the spleen draws 

 off the residual humours from the stomach and in 

 virtue of its blood-like nature can assist in the con- 

 coction of them. If, however, the residue is too 

 bulky or the spleen has too little heat, the stomach 

 gets full of nourishment and becomes diseased. 

 And in many cases, when the spleen is ailing, 

 the stomach becomes hardened owing to the 

 fluid which runs back into it. This happens with 



265 



