CHAPTER I. 



THE NATURE AND REACTIONS OF PROTOPLASM. 



The vital or working substance in every living cell is the 

 protoplasm,* a material which has a very complex chemical 

 and physical composition and constitution. Resolved into its 

 elementary components, dead or " fixed " protoplasm may be 

 said to be made up of Carbon, Hydrogen, Oxygen, Nitrogen, 

 and Snlplmr, and, in the case of the nucleus, in addition, 

 Phosphorns ; these elements are united in certain definite 

 proportions and aggregated into complex molecules or groups of 

 molecules. Certain mineral substances are also always found 

 in close connection with the protoplasm, but not, however, in 

 chemical combination (metaplasm). On the other hand, living 

 protoplasm has probably a ^'ery different constitution as compared 

 with the dead substance, and since it has been found impossible 

 to correctly analyse the living material, its true composition still 

 remains hypothetical ; but chemists have from time to time 

 constructed formulae which have been assumed to represent the 

 composition of dead protoplasm, and which have shown it to 

 be made up mainly of a combination of proteid, amine, and 

 carbohydrate molecules. 



On examining a young living cell microscopically, the proto- 

 plasm appears as a nearly transparent substance, with here and 

 there highly refractive granules ; in the middle of the cell is the 

 nucleus, a specialised portion of the protoplasm, and sometimes 

 there are one or more vacuoles, or fluid-filled spaces, which 

 resemble oil-drops in appearance (see Fig. 1). 



It is probable, as will be seen later, that in many plant-cells the 

 protoplasm is made up of two main portions — viz., a firmer, 

 clearer external part, known as ectoplasm, and a more granular 

 fluid inner part, known as endoplasm ; in cells " fixed " and 



* Termed by Huxley " the physical basis of life" {Method and Results). 



