FOREWORD 



gut passed first to the heart in the form of vapour 

 or serum, and that it was there converted into true 

 blood by a process of concoction. Aristotle knew 

 nothing of the real nature of respiration, and he 

 regarded the lungs as serving to temper the bodily 

 heat by means of the inspired air. He Avas also 

 entirely ignorant of the fact that the blood passes 

 back to the heart and lungs after supplying the 

 tissues and organs with nourishment. On the other 

 hand, he fully appreciated the existence of excretory 

 organs, the function of which was to remove from the 

 body such substances as could not be utilized. In 

 this category are included fluids such as bile, urine, 

 and sweat. In the section on the gall-bladder, as 

 in so many other passages in his works on natural 

 history, it is truly remarkable how correct Aristotle 

 is in his statements. He points out that the gall- 

 bladder is not found either in the horse and ass or 

 in the deer and roe, but is generally present in the 

 sheep and goat. In the light of the knoAvledge that 

 he possessed, therefore, Aristotle could scarcely have 

 adopted a theory about this organ which has found 

 expression in certain modern writings. According 

 to this theory the gall-bladder is present in the sheep 

 and ox because, these being ruminating animals, 

 bile is only required at certain particular times when 

 food passes into the intestine, Avhereas in the horse, 

 which does not cheΛv the cud, but yet is constantly 

 eating, food is continually passing into the intestine 

 and consequently a perpetual flow of bile is desirable. 

 Since the gall-bladder is present in the non-ruminating 

 pig but absent in the ruminating deer and roe, it 

 is obvious that this theory cannot be consistently 

 applied. 



