LIVING SUBSTANCE 117 



all green plant-cells, and cellulose as a protoplasmic product upon 

 the surface of cells. 



The fats also appear to be limited to the protoplasm. Without 

 exception they seem to be wanting in the nucleus, but are very 

 wide-spread in the protoplasm as fat- and oil-droplets. They 

 may always be recognised by their great refracting power, or, 

 in dubio, by their blackening with perosmic acid and solubility 

 in ether. 



Concerning the distribution of the inorganic constituents of the 

 cell almost nothing whatever is known. As to the potassium com- 

 pounds, however, the investigations of Vahlen appear to show that 

 they are to be found exclusively in the protoplasm, and not in the 

 nucleus. 



These are the few facts thus far known. The chemical composi- 

 tion of the great mass of substances in the protoplasm that are 

 termed granules, as well as that of the substances in solution, is 

 thus far wholly unknown. Here an unbounded field is open to the 

 physiological chemists of the future, and in a more distant future 

 shall we have to look to the micro-chemical investigation of living 

 substance for the solution of the final riddle of life. 



The main points of the above examination of living substance 

 may be summarised as follows : Living substance, as it now exists 

 upon the surface of the earth, appears solely in the form of elemen- 

 tary organisms, the cells, some of which live separately, while some 

 Are united together into coherent communities. Each cell 

 is a bit of liquid substance, usually microscopic in size, in which 

 various constituents, partly solid, partly in solution, are stored 

 Only the liquid ground-mass, the protoplasm, and the somewhat 

 more solid nucleus contained within the former can be regarded as 

 general cell-constituents. A bit of protoplasm containing a nucleus 

 is a complete cell, and, vice versa, there are no cells that do not 

 possess nucleus and protoplasm. Just as very different morpho- 

 logical constituents may be distinguished in living substance, so 

 very different chemical bodies are present. The elements of 

 which they consist are only such as exist in the inanimate world 

 also, but their number is small, and it is chiefly the elements 

 having the lowest atomic weights that compose living substance. 

 A special vital element does not exist, but the compounds in which 

 these elements occur are characteristic of living substance, and in 

 great part are absent from the inorganic world. They are, first of 

 all, proteids, the most complex of all organic compounds, which 

 consist of the elements C, H, O, N, and S, and are never wanting 

 in living substance. Further, there occur other complex organic 

 compounds, such as carbohydrates, fats, and simpler substances, all 

 of which either are derived from the decomposition of proteids or 

 are necessary to their construction ; and inorganic substances, 



