B. III.] THE ELISTOBT OF ANIMALS. 69 



from the nose ; when any of these take place, the catamenia; 

 decrease. The blood differs in proportion to the age in quan- 

 tity and appearance, for when very young, it is more like 

 serum, and very abundant ; in the aged it is thick, black, 

 and in less quantity ; in those in the prime of life it is be- 

 tween these. In aged persons the blood coagulates quickly 

 in the body, or on the surface ; but in young persons this 

 does not take place. Serum is imperfect blood, because it 

 has not ripened, or because it has become more fluid. 



CHAPTER XV. 



1. CONCERNING marrow, for this is one of the fluids which 

 exist in some animals. All the natural fluids of the body 

 are contained in vessels, as the blood in the veins, and the 

 marrow in the bones, and others in membranes, skin, and 

 cavities. The marrow is always full of blood in young ani- 

 mals ; but when they grow older, in the adipose it becomes 

 adipose, in fat animals fatty. There is not marrow in all 

 the bones, but only in those that are hollow, and not even 

 in some of these, for some of the bones of the lion have no 

 marrow, others but little ; wherefore some persons say the 

 lion has no marrow at all, as was before observed. In the 

 bones of swine there is very little marrow, in some none at 

 all. 



CHAPTER XVI. 



1. THESE fluids are nearly always co-existent with animal, 

 life ; but milk and the spermatic fluid are produced after- 

 wards. Of these the milk is always secreted in those ani- 

 mals in which it is present. The spermatic fluid is not 

 secreted in all, but in some as in fishes are what are called 

 melts. All animals having milk have it in the mamma3. 

 All animals that are both internally and externally vivi- 

 parous have mamma3, that is, all that have hair, as man, and 

 the horse, the cetacea, as the dolphin, seal, and whale, for 

 these also have mammae and milk. 



2. Those animals that are only externally viviparous, and 

 oviparous animals, have neither mammae nor milk, as fish, 

 and birds. All milk has a watery serum, which is called 

 whey, and a substantial part called curds ; the thicker kinds 

 of milk have the most curds. The milk of animals without 



