Cytoplasm and nuclear material may be stretched to great lengths (with the aid of micro-needles mechanically controlled), and yet return to nearly the original position. Protoplasmic processes formed by cells in tissue-culture, exhibit, on contracting, marked tensile strength and elasticity. Such physical properties owe their existence to a definite type of structure. Polarity and electrical conductance are other properties of protoplasm which rest upon the same structural basis. Systems such as protoplasm, which are contractile and elastic, which show polarity and efficient conductance, possess a linear structural unit capable of an orientation which best fulfills mechanical requirements. The structural unit of cellulose is a long chain (molecule) of glucose residues which are aggregated into bundles (micellae). Chitin, rubber, and silk possess a similar structure. There is every reason to believe that this is also true of albumin, lignin, and reserve substances of a highly polymerized nature and, therefore, also of protoplasm. The most encouraging fea- ture of the problem of the structure of non-living and living matter is that a general type of structure appears to distinguish all systems which have certain physical properties in common. High conductivity means parallel arrangement of linear particles whether we have to do with copper or nerves. The contractile qualities of such jellies as cellulose, rubber, gelatin, and protoplasm are attributable in each case to a long and tenuous structural unit.