PROTOPLASM I I 



17. Chemical Composition of Protoplasm. — It is impossible to make a satis- 

 factory chemical analysis, of living protoplasm, as it loses its characteristic powers 

 and probably undergoes important chemical and physical changes in the act of 

 analysis. The dead material thus obtained is no longer the substance with which 

 we started, either as to its power or its structure. The experiment shows, how- 

 ever, that the substance is both chemically and physically unstable. By an 

 analysis of the dead protoplasm, we find present several complex organic com- 

 pounds, known as proteins, carbohydrates (starches and sugars), /a/i, enzymes, pig- 

 ments, etc. In addition to these are simpler inorganic compounds, as water and 

 various salts. Doubtless some of these materials are food-substances on their 

 way to form protoplasm, and others are the waste-products of protoplasmic dis- 

 ruption, ready to be cast out of the cell. The proteins are the most complex of 

 all these substances and it is believed that protoplasm finds its real basis in them. 



The proteins, which are about 40% of the dry protoplasm, are various in 

 composition and properties, but agree in that their molecules contain carbon, 

 hydrogen, oxygen, nitrogen, and sulphur, in proportion roughly as follows: 

 C 53%, O 22%, N 17%, H 7%, S I %. Carbon is thus the most abundant single 

 constituent element. The white of egg, the fibrin of the blood, and casein in 

 milk are examples of protein. 



Carbohydrates (about 12% of the dry protoplasm) consist of C, H, and O. 

 The latter elements are always present in the ratio in which they are represented 

 in water (H2O), e.g. CeHioOj. The starches, sugars, and cellulose (such as is 

 found in cotton fibres) are illustrations. 



The fats contain the same elements as starch, but the percentage of oxygen 

 in terms of the hydrogen is much smaller than in the starches. These fats com- 

 prise some 12% of the dry protoplasm. 



The enzymes are complex organic substances which have the power of produc- 

 ing important chemical changes in other substances without being themselves 

 consumed. They play an important, but not thoroughly understood, r61e in the 

 activities of the organisms, both within and outside the cells which produce them. 

 The active principle of the digestive juices, as ptyalin and pepsin, are examples of 

 ferments which have been extruded from the cells. 



Water (HjO) is very important in both the chemical and physical structure of 

 protoplasm. It is very variable in amount, and the degree of activity of the 

 protoplasm is 'roughly proportional to the amount of water present. Something 

 like 5-7% of the dry weight of protoplasm is made up of inorganic salts, — com- 

 pounds of chlorine, potassium, sodiun\ calcium, phosphorus, iron, etc., found 

 largely in solution in the water. 



Most of these substances cannot be considered, as "living." The water and 

 inorganic salts and starch cannot be. The starches and fats and urea are organic 

 but not living. If any particular substances are alive it would seem to be the 

 proteins. It may be, however, that life is the result of the intimate relations and 

 interactions of all these various non-living substances rather than a property of 

 any one of them. 



18. The Physical Structure of Protoplasm. — This varies 

 much from time to time. On account of differences in the 

 amount of water present, the consistency of protoplasm may 

 vary from the quite fluid condition found in actively growing 



