22O 



AGE, GROWTH, AND DEATH 



; - " 



seems to me clearly, the effect of differentiation upon 

 the growth of cells. The facts are clear as to their 

 meaning. 



We can, however, proceed a little farther than this, 

 / ^ - ^._ because we can actually ascertain, 



approximately at least, the rate at 

 ^ which cells multiply. We accom- 

 '-'- j plish this by determining the mt- 



u. totic index. The mitotic index is 



I the number of cells to be found at 

 any given moment in the active 

 process of division out of a total 

 of one thousand cells. 



May I pause a moment to recall 

 FIG A 72 ' P r ORTION OK this picture to you and ask you to 



THE OUTER WALL OF A . r J J 



PRIMITIVE MUSCULAR notice at this point the curious 



SEGMENT OF A CAT EM- , , 1-1 



BRYOOF4.6MM. Harvard darker spot which represents a 



Embryological Collection, niir 1 pn< , : n nrnrP cc n f Hiviqinn ? 

 Series 398, Section 115. 11V1S1O 



The resting nuclei are oval, You will SCC it WOuld be easy in 

 pale, and granular. 1 he J 



dividing or mitotic nuclei, such a preparation as this to count 



of which there are three, . , . . .. 



are dark, irregular in out- the nuclei One by One until One 



line, and' show the chromo- i j , i j j . 



somes, in this case the had got up to a thousand, and to 



dividing nuclei all lie near recorc j as onewent along, how 

 the inner surface of the o> 



wall. The picture iiius- many of the nuclei are in process 



trates the ease with which ... . . . 



mitotic figures may be re- of division, for the nucleus in dl- 

 cognised. ... . 1 . . r^-i 



vision is easily recognised. I his 

 process of division is named mitosis : the figure which 

 the nucleus presents while it is undergoing division 

 we call a mitotic figure. Counting the dividing nuclei, 

 we may determine that in a thousand cells there are a 



