IMPORT OF THE NUCLEUS AND CELL-CONTENTS. 37 



of facts in the history of pathological and physiological 

 development, which render it in a high degree probable 

 that the nucleus plays an extremely important part 

 within the cell a part, I will here at once remark, less 

 connected with the function and specific office of the 

 cell, than with its maintenance and multiplication as a 

 living part. The specific (in a narrower sense, animal) 

 function is most distinctly manifested in muscles, nerves, 

 and gland-cells ; the peculiar actions of which con- 

 traction, sensation, and secretion appear to be con- 

 nected in no direct manner with the nuclei. But that, 

 whilst fulfilling all its functions, the element remains 

 an element, that it is not annihilated nor destroyed 

 by its continual activity this seems essentially to 

 depend upon the action of the nucleus. All those 

 cellular formatioiid which lose their nucleus, have a 

 more transitory existence ; they perish, they disap- 

 pear, they die away or break up. A human blood cor- 

 puscle, for example, is a cell without a nucleus ; it pos- 

 sesses an external membrane and red contents ; but 

 herewith the tale of its constituents, so far as we can 

 make them out, is told, and whatever has been recounted 

 concerning a nucleus in blood-ceils, has had its founda- 

 tion in delusive appearances, which certainly very easily 

 can be, and frequently are, occasioned by the production 

 of little irregularities upon the surface (Fig. 52). We 

 should not be able to say, therefore, that blood-corpuscles 

 were cells, if we did not know that there is a certain 

 period during which human blood-corpuscles also have 

 nuclei ; the period, namely, embraced by the first 

 months of intra-uterine life. Then circulate also in the 

 human body nucleated blood-cells, like those which we 

 see in frogs, birds, and fish throughout the whole of their 

 lives. In mammalia, however, this is restricted to a cer- 

 tain period of their development, so that at a later stage 



