Nothing illustrates better the patience of Darwin, and of course also of hundreds of other scientists who are working as he worked in unknown laboratories all over the world, than the process of simple waiting so often necessary to obtain results. Nature demands time, often enormous time, and the brevity of human life and the evanescence of human opportunity mean nothing to her. The careful working out of scientific investigation requires the study of successive generations, sometimes of many, the sowing of the seed and the gathering of the blossom, the close observation of the individual from conception to death, which can be carried on only through long periods of time. The observer must keep a dozen lines of study in his mind, must maintain them side by side, and must be always ready to turn from one to the other, as some new development arises that demands his attention. It was in this phase of long, renewed, continued, enduring watchfulness that Darwin was preëminent. As well appears in his son’s record: ‘I think it was all due to the vitality and persistence of his mind—a quality I have heard him speak of as if he felt that he was strongly gifted in that respect. Not that he used any such phrases as these about himself, but he would say that he had the power of keeping a subject or question more or less before him for a great many years.’[43] Very little examination of Darwin’s books is required to show how amply and constantly this power was exercised. And to give such patience and taste for continuity their full effect there is needed almost a passion for system, for orderly arrangement, and the habit of putting not only things but thoughts in their proper places, so that they can be called upon at the right moment in the right way. Darwin himself describes his elaborate method of indexing the books that he read and the notes that he made, so that whenever he wished to deal with any special subject, he could turn at once to material bearing upon it: ‘Before beginning on any subject I look to all the short indexes and make a general and classified index, and by taking the one or more proper portfolios I have all the information collected during my life ready for use.’[44] Such systematic habits of working both demand and imply an orderly and economical use of time. Owing to his limitations of health, Darwin’s working time was extremely limited, but he made the most of it. Every usable hour was allotted, and the utmost profit and result were extracted from it. No doubt such sense of pressure is in itself not very beneficial to health, but it means an immense amount of work accomplished. The time was employed thriftily as well as intelligently: ‘He saved a great deal of time through not having to do things twice.’[45] And everywhere there is the feeling of the value of minutes which is indicated in Dante’s saying, Chè’l perder tempo, a chi più sa, più spiace.[46]