62 PATHFINDERS OF PHYSIOLOGY 



position and added that the cell consisted of little units of protoplasm 

 surrounding" a nucleus. The nucleus was first described by Fontana, 

 in 1871. It was regarded as a normal element of the cell by Robert 

 Brown in 1883. It was eventually seen that many cells, especially 

 animal cells, are without a cell wall, hence the conclusion that the so- 

 called "wall" is not an essential feature of the "cell." When the cell 

 wall is absent the protoplasm is the cell. The nucleus was found to 

 be within the substance of the cell and not within the cell wall. 

 Schultze -defined the cell as a globule of protoplasm surrounding a 

 nucleus. From being regarded as an element of structure merely, the 

 cell has come to be recognized as the physiological unit within which 

 all physiological activity takes place. 



Perhaps the most authoritative as well as the most recent defi- 

 nition of protoplasm is the following significant paragraph by Star- 

 ling: 



"Though it may be convenient to have a word such as protoplasm signifying 

 simply 'living material,' it is important to remember there is no such thing as a 

 single substance — protoplasm. The reactions of every cell as well as its organiza- 

 tion are the re,sultant of the molecular structure of matter of which it is built up. 

 The gross methods of the chemist show him that the composition of the proto- 

 plasm 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 peculiarities 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 reactions of it's 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 to the life of the cell and both must 

 be regarded 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 proto- 

 plasm or as products of the break down of protoplasm; but in many cases it is 

 impossible to say whether a given material is to be regarded as lifeless or as re- 

 active living matter. Even in a single cell we may have differentiation among 

 its different parts, one part serving for the process of digestion while other parts 

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

 differences, and therefore dtflerent protoplasms." 



A statement of the cell theory at the present time (1913) must 

 include four conceptions: (1) The cell as a unit of structure; (2) The 

 cell as a unit of physiological activity; (3) The cell as embracing all 

 hereditary qualities within its substance; (4) The cell in the histori- 

 cal development of the organism." 



Students of cytology have sought to find out if any uniformity 

 of organization of protoplasm exists. Accordingly we have a number 

 of explanations or theories regarding its structure. Altmann pro- 

 posed the granular theory. By the employment of certain hardening 

 reagents he demonstrated dense masses of spherical or rod-shaped 

 granules in all the cells of the body. In these he located the various 

 vital functions, the sum total of which constitute the life of the cell. 



