ARISTOTLE'S HOMCEOMERIA. Ill 



statements about the formation of flesh, after consulting 

 this Hippocratic treatise. It is admitted, however, that this 

 treatise was not written by Hippocrates, but by an author 

 of much later date. Plato also says that flesh is normally 

 formed from the blood,* but his real meaning is not clear, 

 for he says that bone, flesh, and the like are all formed 

 from marrow and other materials. t 



Aristotle does not appear to have known anything about 

 that most remarkable property of flesh, viz., its contractility. 

 This will be discussed in Chapter xiii. His reference to 

 " fibres " and the like seen in flesh show that he saw, but 

 did not understand the nature of, the connective tissues 

 which ensheath the muscle-bundles. 



6. Suet and Fat. — Aristotle says that suet is quite hard 

 and brittle when cold, but fat is liquid and does not harden, 

 and that they differ with respect to the parts in which they 

 occur, t Both suet and fat are formed, according to him, 

 from blood, and, on this account, he concluded wrongly that 

 fat is not found in animals without blood. § 



Aristotle's statement that fat is liquid and does not 

 harden is true of some animals only. The comparatively 

 large masses of fat in geese, ducks, and quails are nearly or 

 quite liquid in the living birds, and the fat of the quail 

 runs like water at as low a temperature as 50° or 60° F. 

 The fat of fishes and amphibians is also fluid at compara- 

 tively very low temperatures. The fat of some animals 

 melts at comparatively high temperatures and, even in 

 animals like pigs and horses, in which the fat is of a soft 

 kind, it is not liquid in the living animals. 



7. Marroio. — In P. A. ii. c. 6, 6516, Aristotle says: 

 " Marrow is of the nature of blood and is not, as some 

 believe, the active generating force of semen." This is a 

 refutation, more particularly of one of Plato's statements in 

 the TimcBUs, 73. It is contained, he says, in the bones, and 

 is quite full of blood in young animals, but is either fatty or 

 suety in older animals. tl 



In very young animals the marrow is red and vascular, 

 and in older animals there are the ordinary yellow marrow, 

 rich in fats, and the red marrow found in the ribs, sternum, 

 vertebrae, cranial bones, and the epiphyses of the long 

 bones. This red marrow contains less fat, but many small 



* TimcBus, 82. \ Ibid. 73. 



\ H. A. iii. c. 13, s. 1. § P. A. ii. c. 5, 651a. 



II H. A. iii. c. 15. 



