Development and Growth of the Epidermis. 87 



evident also that the nuclei, up to a certain point, grow with 

 the cells, their mode of growth appearing to be, the separa- 

 tion of the original granules by the deposition between them 

 of interstitial matter; and in addition, as I believe, by clea- 

 vage of the latter and the consequent multiplication of the gra- 

 nules. In cells measuring ^imo 10 ant ^ Tiioo tn °^ an mcn > ' 

 found the granular character of the nucleus to be very mani- 

 fest. Besides growth, it is apparent that 'other changes are 

 taking place in the nucleus ; imbibition and assimilation of or- 

 ganisable material must necessarily be in action in order to 

 accomplish the formation of interstitial matter; but in addi- 

 tion to this the central granules undergo another change, by 

 which they are altered in character and become distinguished 

 from the rest when submitted to chemical experiment. For 

 example, when dilute acetic acid is added to the cells measu- 

 ring TTTroTrth of an inch and less, the entire nucleus is rendered 

 transparent and less discernible than before; but when cells 

 of a somewhat larger size, and consequently longer growth, 

 are submitted to the same process, the nucleus is rendered 

 much more distinct than it was previously. But the body 

 which is made so conspicuous in this latter experiment is not 

 the entire nucleus, but simply the central and older granules 

 of the nucleus ; the younger granules retain the character of 

 those of the young cells, they are made more transparent than 

 they were before, and have faded from sight. I may mention 

 also, that the nucleus brought into view by the acetic acid is 

 more or less irregular in form, and has the appearance of being 

 constituted by the fusion of the original granules. How much 

 of this appearance may be real and how much the effect of the 

 acid, I do not pretend to say, and I set no value on the ex- 

 periment beyond the demonstration of the mere fact which it 

 is made to illustrate. 



I now turn to the growth of the cells. I have remarked, 

 in an earlier paragraph, that the formation of the young cell 

 appears to be due to the development of a stratum of "aggre- 

 gated granules" externally to the nucleated mass, which I 

 have regarded as the cell-nucleus. Now nothing is more cer- 

 tain than that the growth of the cell is due to a successive re- 

 petition of this process, the growth of the cell-membrane being 

 consentaneous with the development and growth of " aggre- 

 gated granules" within it. In cells of TT j\nj tn ^tjVo 10 OT>an 

 inch, the "aggregated granules" of the periphery are not 

 easily discernible; but in cells measuring y^^th, and thence 

 upwards to the complete size of the epidermic cell, the fact is 

 quite evident, and is apparent even in the cell-scale. Indeed 

 a cell, at the lull period of growth, is a kind of cell-microcosm, 



