OKLAHOMA ACADEMY OF SCIENCE 45 



The perioptican is so closely connected to the eye itself that it 

 i-; not surprising that it should be wanting in the totally eyeless, 

 but it does seem surprising to find so much of the optic tract left 

 when it no longer has any function. 



XXI. THE MITOTIC INDEX OF THE CHICK 

 Audrey Flitch Shultz. 



Fr.)m the Zoological Laboratory of the University of Oklahoma. 

 Contribution No. 18, Second Series. 



Introduction 



Grov/th and its relation to differentiation has long been one of 

 iIk' perplexing problems of biology. Most scientists believe that 

 the highest rate of growth occurs ih the earlier stages of the organ- 

 ism and as differentiation takes place that rate is correspondingly 

 lessened. But the problem is to prove this. 



Minot in his book on "Age, Growth and Death" suggested a 

 method. He counted the number of cells in the active process of 

 division out of a total of one thousand. This he called the mitotic 

 index. With this plan in mind I attempted to determine the mitotic 

 indices of the 18-20, 33, 48 and 72 hour chicks. However, I changed 

 the definition of the term mitotic index to mean the number of 

 cells found in the active process of division out of a total of one 

 hundred instead of one thousand, thus making the term mitotic 

 index synonymous with rate and percentage. I might equally well, 

 if not better have called this paper the mitotic ratio of the chick. 



Materials and Methods 



Prepared serial transverse sections of each of the above named 

 stages were examined with an oil immersion lens and the nuclei 

 counted, one by one, in each section of each chick series. Records 

 were made during the progress of the work of the number of 

 nuclei which were in a process of division. With these figures I 

 was able to determine mathematically the percentage of cell divi- 

 sion for the separate parts of the germ layers of each section. I 

 then added up all the dividing and non-dividing cells of these sec- 

 tions. With these totals I figured the rate of cell multiplication of 

 each germ la5'er and of the chick as a whole. In this paper I 

 shall very briefly discuss the results of each chick stage separately, 

 then draw conclusions from a comparison of all four of them. 



18- 20-Hour Chick 



The 18-20 hour chick, a stage preceeding the differentiation of 

 organs, shows a very high percentage of cell division having a mito- 

 tic index of 4.139. That is out of every one hundred cells an 



