Fishes are next discussed with nearly equal brevity. He remarks, that they have a peculiar elongated form, are destitute of mammae, emit by their gills the water received at the mouth, swim by means of fins, are generally covered with scales, and are destitute of the organs of hearing and smelling. His description of the internal parts of these tribes of animals contains a mixture of truth and error. This book terminates with remarks on the structure of serpents. The third commences with observations on those parts of animals which are homogeneous, such as the blood, the fibres, the veins, the nerves, and the hair. Under the general title of nerve, he confounds the columnae carneae of the heart, the tendons and fasciae; and it does not appear that he had any idea of what modern anatomists call nerves. In speaking of hair, he remarks that it grows in sick persons, especially those labouring under consumption, in old people, and even in dead bodies. The same remark applies to the nails. The blood is contained in the veins and heart, is, like the brain, insensible, flows from a wound in any part of the flesh, has a sweet taste and a red colour, coagulates in the air, palpitates in the veins, and when vitiated is productive of disease. On the subject of milk, his observations deserve attention. Thus, he says that all viviparous animals which have hair are furnished with mammae, as are also the whale and the dolphin; but those which are oviparous are not so provided. All milk has a watery fluid, called serum, and a thick part, called cheese; while that produced by animals which are destitute of fore teeth in the upper jaw coagulates. On this subject he mentions some curious circumstances. Some kinds of food occasion the appearance of a little milk in women who are not pregnant. There have even been instances of it flowing from the breasts of elderly females. The shepherds about Mount Oeta rub the udders of unimpregnated goats with nettles, and thus obtain abundance of milk from them. It sometimes happens that male animals secrete the same fluid; thus, there was a he-goat in the island of Lemnos, which yielded so much that small cheeses were made of it. A little may be pressed from the breasts of some men after the age of puberty; and there have been individuals who on being sucked have yielded a large quantity. Instances of this have been recorded by other observers; and Humboldt met with a similar case in South America.[D]