110 AEISTOTLE'S HOMCEOMERIA. 



His attempts to describe the structure of these blood- 

 vessels can hardly be expected to be satisfactory. He noticed, 

 however, that the walls of the arteries were stouter than 

 those of the veins, but his explanation is incorrect. The 

 walls of arteries and veins are similar in structure, but there 

 is a much greater development of muscular and elastic 

 tissues in the inner and middle coats of the walls of the 

 arteries than in those of the veins. In the passage already 

 referred to, from H. A. iii. c. 3, s. 3, Aristotle probably 

 uses the term membrane for the inner coat of the venae 

 cavae, which is somewhat readily separable from the middle 

 coat. 



In H. A. iii, c. 5, s. 3, it is said that the material forming 

 blood-vessels can resist the action of fire, while sinew is 

 entirely destroyed by it. This statement is not altogether 

 fanciful, for, when pieces of the aorta of an ox are cut off 

 and placed on a bright red fire, except that they very slowly 

 carbonize with the formation of small blisters and the 

 oozing out of a small quantity of fluid, their forms undergo 

 as little alteration as if they were pieces of porcelain. Under 

 the same conditions, sinews are at once twisted into fantastic 

 shapes and are carbonized more rapidly. 



4. Shin and Memhi'ane. — There is but little information, 

 in Aristotle's works, about these materials. He considered 

 skin i^^pf^a) to be fissile and extensible, and membrane (ufxriv) 

 to be of the nature of a thin, compact skin, but neither fissile 

 nor extensible.* He also says that membrane does not re- 

 unite after it has been cut.t He includes the urinary 

 bladder among membranes, but says that it is of a special 

 kind, because it is extensible, t 



5. Flesh. — This is included by Aristotle among the soft 

 or fluid homoeomeria. Flesh, he says, is fissile in all direc- 

 tions, § and is a material thrown down from the blood which, 

 contained in numerous blood-vessels, is so universally dis- 

 tributed through the flesh that blood flows at once from any 

 part of the flesh when cut, even though the blood-vessels 

 cannot be seen in the cut parts. || 



In the Hippocratic treatise. On Flesh, §§8 and 9, it is 

 explained how the liver, the kidneys, and the flesh are 

 formed as a result of some kind of coagulation of the blood. 

 It would seem, at first sight, that Aristotle had written his 



- H. A. iii. c. 11, s. 1. j Ibid. 



I Ibid. iii. c. 11, s. 3. § Ibid. iii. c. 12, s. 1. 



II P. A. iii. c. 5, 668a. 



