COMPOSITION OF PROTOPLASM. 



79 



chemical compounds which behave essentially like common egg-albumen, or the 

 casein of milk, or like the coagulable substance of blood, &c. These chemical 

 compounds are composed of the elements carbon, hydrogen, oxygen, nitrogen, and 

 sulphur : they are the most complex of all organic chemical combinations, and 

 as the result of their decomposition a large number of simpler organic carbon com- 

 pounds are formed. The statement that protoplasm consists of albuminous sub- 

 stances is, however, not to be understood to mean that proteid and proto- 

 plasm are identical. For by the former is meant only the chemical compound 

 of the elements mentioned; whereas the protoplasm composed of this pos- 

 sesses a definite organisation, which is foreign to the chemical compound as 

 such. The case is similar to that of the chemical compound of chlorine and 

 sodiiun (common salt) on the one hand, and, on the other hand, of the 

 crystals of common salt. It is, moreover, only an abbreviation to say that 

 protoplasm consists of proteids. 

 This is only its essentially distinc- 

 tive character; but, as. a matter 

 of fact, living protoplasm always 

 contains a larger or smaller quan- 

 tity of water, and if this is with- 

 drawn up to a certain minimum 

 it loses its vital activity, and on 

 the withdrawal of more water even 

 its ability to live. The water be- 

 longs to the molecular structure of 

 the living protoplasm in the same 

 sense as the water of crystallization 

 is necessary to the structure of very 

 many crystals, which lose their crystal- 

 line form on the withdrawal of the 

 water of crystallization. 



On examination we find, more- 

 over, that in the protoplasm mineral 

 constituents are further contained, 

 which, after its combustion, remainover 

 as incombustible ash; a series of salts 



in which alkalies, lime, magnesia, phosphoric acid, and sulphuric acid predominate. 

 Even so far, the protoplasm appears to be a mixture of numerous chemical 

 compounds; and we have cause to believe, in addition, that continual chemical 

 changes are connected with the vital processes in it, the products of which remain, 

 at least for a time, between the molecules of the protoplasm. The substance of the 

 protoplasm here described appears quite homogeneous under the microscope, even 

 with very strong magnifying powers. In actively vegetating cells, however, this 

 substance, in itself homogeneous and transparent, is thickly set with very numerous 

 small granules (microsomes); these appear even with the strongest magnifying 

 powers as dots, the true nature of which, from a chemical point of view, and 

 the importance of which for the life of the protoplasm, are still doubtful, although 



FiG. 76.— Forms of the protoplasm enclosed in cells A and B of 

 Zea Mays. A cells from the first leaf-sheath of a seedling ; S from the 

 first intemode of the same ; Cfrom the tuber of HeliatUkus iitberosiis, 

 after the action of Iodine and dilute Sulphuric acid ; A cell-wall ; 

 k nucleus ; / protoplasm. 



