16 PHYSIOLOGY 



' protoplasm ' of the muscle cell is entirely different from that of a leucocyte 

 or white blood corpuscle. The finer methods of the physiologist show him 

 that every sort of cell in the body has its own manner of life, its own pecu- 

 liarities of reaction to uniform changes in its surroundings. No individual 

 will react in exactly the same manner as another individual, even of the 

 same species, and the reactions of the whole organism are but the sum of the 



Attraction-sphere enclosing two centrosomes 



Nucleus- 



Plasmosome 



or true 

 nucleolus 



Chromatin- 



network 



Linin-network 



Karyosome 

 net-knot, or 

 chromatin- 

 nucleolus 



Plastids lying in the 

 cytoplasm 



Vacuole 



Passive bodies (metaplasm 

 or paraplasm) suspended 

 in the cytoplasmic mesh- 

 work 



FIG. 3. Diagram of a cell. Its basis consists of a meshwork containing numerous minute 

 granules (microsomes) and traversing a transparent ground-substance. ( WILSON.) 



reactions of its constituent cells. There is not one protoplasm, therefore, but 

 an infinity of protoplasms, and the use of the term can be justified only if we 

 keep this fact in mind and use the word merely as a convenient abbreviation 

 for any material endowed with life. Even in a single cell there is more than 

 one kind of protoplasm^. In its chemical characters, in its mode of life, 

 and in its reactions, the nucleus differs widely from the cytoplasm. Both 

 are necessary for the life of the cell and both must be considered, according to 

 our present ideas, as * living.' In the cytoplasm itself we find structures or 

 substances which we must regard as on their way to protoplasm or as products 

 of the breakdown of protoplasm ; but in many cases it is impossible to say 

 whether a given material is to be regarded as lifeless or as reactive living 

 matter. Even in a single cell we may have differentiation among its different 

 parts, one part serving for the process of digestion while others are 

 employed for the purpose of locomotion. Here again there must be chemical 

 differences, and therefore different protoplasms. In this work the term 

 protoplasm will be used in its broadest sense, namely, as the physical basis 

 of living organisms. 



STRUCTURE OF THE CELL. In every cell can be distinguished the 

 two parts nucleus and cytoplasm. The nucleus is generally an oval or 



