368 EOSS — ON THE FIBEIN OF THE BLOOD. 



development of any organism consists in the multiplication and 

 addition of cells and their modification into the several tissues, 

 while nutrition consists simply in the replacing the worn out cells 

 by new ones, and the assimulation of these with the tissue into 

 which they have been incorporated. Cells are of two kinds — 

 primordial and derived — the primordial being the result of the 

 union of oil albumen combining according to their reciprocal affini- 

 ties, and the derived resulting from the development of the nucleus 

 which appear soon after their formation. 



The experiments* of Ascherson shew that the simple contact of 

 oil and albumen at the ordinary temperature of the blood of animals, 

 immediately results in the formation of cells, of which the albumen 

 forms the envelope, and the oil the contents. Cells so formed, 

 artificially, resemble so closely, as to seem identical with, the pri- 

 mordial cells produced within the animal, but pass through none 

 of those phases of development which characterize the latter. 



Researches on the formation of the egg in the various classes 

 of the animal kingdom, have shewn that there is a time in its 

 history when it cannot be distinguished from the ordinary cells 

 constituting the organic tissues. It however undergoes a special 

 development. Nuclei appear in its interior, and are developed into 

 true cells which similarly develop within them new cells. When 

 the third generation of cells has appeared, the first cell envelope 

 disappears, setting free its contents. And this process goes on 

 until the mass of cells which constitutes the vitellus or yolk of the 

 egg is produced. It is well known that the white of the egg with 

 which we are familiar in the eggs of fowl is merely a supply of 

 albumen provided for the nourishment of the chick, and like the 

 calcareous covering which in such eggs constitutes the final en- 

 velope, is not a necessary adjunct to an egg. In the white of the 

 egg, when it exists, " floating cells " are found, which have become 

 detached from the vitellus, and consequently undergo an abnormal 

 development. Similar "floating cells" are found in the vitellus 

 during the progress of segmentation. 



* Archives of Anatomy, Physiology, and Medicines, edited by J. Muler, 

 Berlin, 1840, p. 44. 



