the doctrine, and belonged rather to the way of conceiving that the evolution of organisms has taken place. Looking not for differences but relationships among organisms, I thought I saw that a simple and general law had governed their formation, that they were derived one from another by a constant procedure, and I found myself adding further arguments to the theory of the genealogical origin of species. The law which I now have to put forward may be called the law of association; and the process by which it works, the transformation of societies into individuals.
When we have proved that all living beings are composed of microscopic corpuscles more or less alike, when we see such corpuscles capable of leading an independent life constituting by themselves the simplest organisms, it occurs to us to compare the higher animals and vegetables to vast associations of distinct individuals, each represented by one of these corpuscles or cells. In the same animal the cells assume many different forms, having different physiological properties. These forms and properties are not modified by the vicinity of different cells. Within the organism each cell lives as if it were alone. If it were possible to isolate a cell of the human body and surround it by normal nutritive material, it would continue to live, to develop and reproduce itself, and carry on all its physiological functions exactly as before. Further, in the organism itself, the life of each cell is so independent of that of its neighbors, that we may kill all the cells of one kind without injuring the others. Claude Bernard has proved that curare poisons the elements that terminate the motor nerves, thus abolishing all movement without injuring any other part of the system and leaving sensation intact. These researches led him to the principle of the independence of the anatomical elements. Not only are the elementary individuals of organisms sometimes very dissimilar, but they preserve their personality, live their own way, and keep up with their fellow citizens the relations of good neighborhood. We may compare an animal or plant to a populous town, where each person practices a particular industry on his own account, and yet helps the general prosperity through the activity of exchange. In high organisms, a special corporation in ceaseless movement is the medium of these exchanges. The blood-globules are true traders, taking along in the liquid where they swim the complex merchandise in which they deal.
Just as we had employed all the comparisons that pedigree furnishes to express the likenesses among organisms before supposing them really to be blood relations, so we have compared organisms to societies and societies to organisms, all the while regarding these comparisons as mere fancies. On the contrary, in the last year, we have reached the conclusion that association has played an important if not exclusive part in the development of organs. We find convincing proof of this in the history of Polyps and of Worms. The connection
