A modern medical authority, Sir Henry Thompson of London, in his book, “Diet in Relation to Age and Activity,” takes somewhat similar ground, although careful to state that he is not “a vegetarian.” He says: “I have been compelled by facts to accept the conclusion that as much mischief in the form of actual disease, impaired vigor and shortened life accrues to civilized man, so far as I have observed in our own country and throughout almost every part of Europe, from erroneous habits in eating as from the habitual use of alcoholic drink, considerable as I know the evil of that to be.” [9] [9] See chap. xxi on “Natural Living.” CHAPTER XXVIII MORE THEORIES To Sleep I give my powers away My will is bondsman to the dark; I sit within a helmless bark. TENNYSON. There is another class of investigators who aim to explain what might be called the nervous mechanism of sleep rather than its causes. These are the histologists, and theirs is the “histological” theory of sleep. There is a vast literature on this one phase of sleep theorizing alone, and it is deeply interesting to those who, in order to understand this theory, are willing to wrestle with the difficult and technical terms. The general reader, unfamiliar with physiological terms, is bewildered by such a word as “neuroglia.” He wonders what sort of a fossil that is, when in fact it is merely a particular sort of tissue found in the central nervous system; a substance without any nervous property serving a purpose merely similar to cement. So that, after all, like much science, it is simple enough when put in plain words.