14 PHYSIOLOGY. 



Because of its influence in the cell, it has aroused more interest 

 among investigators than any other component of the- cell. By some 

 it is considered to be a part of the nucleus, and by others, of the pro- 

 toplasm. As a rule, it lies in the protoplasm just outside of the 

 nucleus, even during the resting stage, and in certain conditions of 

 the cell is clearly indicated by a radiation of protoplasm, attraction 

 sphere, or archoplasm, the fibers of which are arranged in the form of 

 a star, the centrosome being at the center. 



In size the centrosome ranges between that of the ordinary micro- 

 some and the smallest micro-organism. No structure has been as yet 

 discovered in it. It cannot be classed as a general cell-constituent, 

 since many forms of the cell and unicellular organisms have been 

 examined and no centrosome found, due probably to the inadequacy 

 of the microscope. Most authors consider the centrosome as an essen- 

 tial part of the cell. 



The centrosome does not absorb the ordinary stains suitable for 

 the nucleus, but requires acid anilin dyes, as acid fuchsin and 

 orange. By them it is colored vividly. 



As a rule, there is one centrosome in a cell, lying close to the 

 nucleus and surrounded by a raylike or rodlike structure of the pro- 

 toplasm. As the cell prepares for division, the centrosome divides 

 into two distinct parts, both lying passively within the starlike net- 

 work. When the daughter-cells are examined, each is found to pos- 

 sess one of the centrosomes, which, as the cell grows, passes through 

 the same process as its antecedents. The centrosome is regarded as 

 the particular organ of cell-division. 



PROTOPLASMIC MOVEMENT. 



The movements of protoplasm are movements in currents and 

 the amoeboid movement. In certain vegetable cells protoplasm moves 

 and causes a true rotation of its substance, as in Chara ; or the move- 

 ment may be in opposite direction and the paths even cross over each 

 other. In this movement all parts of the protoplasm do not move 

 with the same rapidity. The rate in protoplasm is about 1 / 50 inch 

 per minute. 



Movements differ according to whether the protoplasm is naked 

 without any enveloping membrane or' inclosed within a firm wall, 

 or membrane. 



