The science of life : fully illustrated in tone and line and including many diagrams

WEARING OUT OF MACHINE AND ITS REPRODUCTION

living matter is potentially immortal. If one keeps a culture from the tissue of a young animal and takes sub-culture regularly, the race of cells can apparently go on growing and dividing indefinitely. Death is a consequence of incomplete organization ;

Fig. 56. (above), and a great age (below).

The lower jaw at the prime of life

the tissues die because they are parts of an imperfectly balanced body.

How far it may be possible for a body to sustain its balance and continue indefinitely or at least for a much longer period than the normal life of its species, is an interesting matter for speculation. Such a prolongation is not Nature’s ordinary way. But there are long-lived species which do remain recuperative for relatively long periods. Parrots will last out eighty years and eagles ahundred, and such a fish as the carp, especially if it is protected from external danger in a garden pond, seems able to go on almost without a limit. There is evidence for hundred-andfifty-year-old carp and for pike which have lasted for two centuries. Some trees have an enormous span of life. The baobab of Cape Verde is supposed to endure five

thousand years, and the Sequoia gigantea of California almost as long.

The prolongation of the restless, various human life is a much more complex issue than that of keeping alive a captive bird or fish. Many old people are still hungry for experience, and the fact that the intelligence outlasts many other bodily powers gives the death of ripe-minded and balanced men and women a quality of tragic waste. From what we have said and from what we will explain a little later, it will be plain that the process of old age is at least partly chemical and accompanied by defects of internal secretion. But it is not by any means a simple process ; this man gives first at one point and that man at another, and the replacement or reinforcement of the secretion that would help in the first instance might simply intensify the want of balance in the second. Ilya Metchnikov was disposed to ascribe many of the phenomena of senility to decay in the large intestine, and sought to correct this by a liberal use of koumisssoured milk, such as the long-lived Tartars consume—which abounds in bacteria whose products check intestinal putrefaction. For a time koumiss was a fashionable drink among the elderly, but after the death of Metchnikov, at the age of seventy-one, faith in his remedy declined.

In the young and developing adult certain secretions from the interstitial tissues of the

Fig. 57. Nerve cells from the brain of a youth af sixteen (left), and of an old man (right). The old cell is filled with droplets of fat (shown black).

reproductive glands play an invigorating part in the growth and strengthening of the body, and various experimenters have tried to restore the dwindling supply of these secretions as age comes on. Steinach seeks