This section is from the book "The Dogs Of Great Britain, America, And Other Countries. Their Breeding, Training, and Management in Health and Disease", by John Henry Walsh (Stonehenge). Also available from Amazon: The Dogs Of Great Britain, America And Other Countries.
The muscles of the dog have nothing remarkable about them, except that they are renewed and wasted faster than in most 13 animals. This has passed into a proverb, and should be known as influencing the time which dogs take to recruit their strength.
The nervous system is highly developed in those breeds which have been carefully attended to, that is, where individuals of high nervous sensibility have been selected to breed from. This is therefore remarkable in the bulldog, selected for generations for courage; in the pointer, where steadiness in pointing has been the prominent cause of choice; and in the greyhound, whose characteristic is speed; all requiring a high development of the nervous system, and all particularly liable to nervous diseases, such as fits, chorea, eta On the other hand, the cur, the common sheep-dog, etc., seldom suffer from any disease whatever.
The stomach of this animal is extremely powerful in dissolving bones, but it is also very liable to sickness, and on the slightest disturbance rejects its contents. This appears to be almost a natural effect, and not a diseased or disordered condition, as there is scarcely a dog which does not wilfully produce vomiting occasionally by swallowing grass. Few medicines which are at all irritating will remain down, and a vast number which are supposed to be given are not retained on the stomach, while others are only partially so. The bowels are extremely liable to become costive, which is in great measure owing to the want of proper exercise, and this also is very apt to produce torpidity of the liver. It may, however, be observed that in almost all particulars, except the tendency to vomit, the digestive organs of the dog resemble those of man.
There is nothing whatever remarkable in the heart and lungs; but the blood-vessels, like those of most of the lower animals, are so elastic in their coats that they quickly contract when divided, and a fatal bleeding rarely results.
The skin of the dog is said to be quite free from perspiration, but this is a mistake, as I have often seen the short hairs of a smooth-coated dog glistening with fine beads of liquid, poured out on a hot day, when strong exercise was taken. The tongue, however, is the grand means of carrying off heat by evaporation, and its extensive surface, when hanging out of the mouth, is sufficient for the purpose, as the fluid is carried off more rapidly from the air passing over it in expiration. I am persuaded that a considerable amount of insensible perspiration is constantly going on from the surface of the skin, and that nothing ought to be done which is likely to check it. This, however, is contrary to the generally received opinion, which is that nothing of the kind takes place in this animal.