The homoeomerous parts and their replacement by Bichat's tissues.

Bichat (1801) developed a set of twenty-one distinguishable tissues into which the whole human body could be divided. ' This paper seeks to distinguish his set from its predecessor, the Homoeomerous Parts of the body, and to trace the transition from the one to the other. The earlier comparable set of distinguishable components of the body was the Homoeomerous Parts, a system founded according to Aristotle by Anaxagoras (about 500-428 BC),2 and covering not just the human body, or living bodies generally, as Bichat's tissues did, but the whole material world. "Empedocles says that fire and earth and the related bodies are elementary bodies of which all things are composed; but this Anaxagoras denies. His elements are the homoeomerous things (having parts like each other and like the whole of which they are parts), viz. flesh, bone and the like." A principal characteristic of a Homoeomerous Part is that it is indefinitely divisible without changing its properties; it can be chopped up very finely to divide it, but is not otherwise changed in the process. The parts are like each other and like the whole Part, but not actually identical. Limbs, in contrast, obviously do not qualify; they cannot be chopped into littler limbs. Aristotle starts his own explanation with the example of minerals: "By homoeomerous bodies I mean, for example, metallic substances (e.g. bronze, gold, silver, tin, iron, stone and similar materials and their by-products) ...;'3 and then goes on to biological materials: "and animal and vegetable tissues (e.g. flesh, bone, sinew,4 skin, intestine, hair, fibre, veins) from which in turn the anhomoeomerous bodies-face, hand, foot and the like-are