conditions, for the fountain of action escapes them as the fountain of youth receded before the searching eyes of Ponce de Leon. Nevertheless, the treasures on the road of the deluded are no less valuable than those strewn on the pathway of the sane, if they will but pick them up, and all the wealth of our much boasted “causal” biology has been brought home by men who were not lucky enough to get what they were after, but wise enough to take what they could find.
Those who have parted with their entire wealth of prejudice in the matter of causation can safely begin to discuss the question whether scientific explanations, explanations by means of chains of events, can be legitimately applied to vital action, and furthermore whether such explanations are useful. At the outset, however, they meet with a grave difficulty, for at the present time no one knows exactly what it is that needs to be explained. Some tell us, life is motion; others call it a chemical-physical process; whereas some declare it synonymous with consciousness. Herbert Spencer, after cudgeling his brains for many years, arrived at a statement which seemed to him, as it has to many since then, the best possible. “Life,” he says, “is the continuous adjustment between internal relations and external relations.”
Unfortunately none of these definitions is really satisfactory. Who, on being told that life is the continuous adjustment between internal and external relations, can feel that now he has the secret firmly in his grasp? Indeed at present a hard and fast definition is scarcely possible, and, if it were, would add more to the comfort of the dialectician than to the progress of knowledge. When we understand life the definition will come of itself, and then no one will care to use it.
Most of the biological work of to-day is an attempt to find out exactly how living things make their living, and the biologist, regardless of his party affiliations, is happy to say that all who study these questions agree that living things make use of machinery. Is not the respiratory system a machine by which oxygen is taken from the air and carbon dioxid given off to it? Is not the digestive system a factory which changes food-materials into simpler compounds that are absorbed?
The machinery of living things is very remarkable, complex, and adequate. It may not always be wholly adequate, but certainly in general it is sufficiently so. Sometimes it can be improved by surgery, by the prescription of glasses, hearing trumpets, false-teeth and tonics, but on the whole it is adequate, it is fit. Indeed, fitness more or less pronounced, but fitness, nevertheless, is the leading characteristic of living machinery and its processes, and under shifting external conditions, distinguishes them clearly from things not alive. No man need take the time to adjust himself consciously when he deals with his fellowmen, with horses, dogs and with building materials. Our famil-
