CELL FORMATION. 347 



more ; these enclose what are termed the nucleoli. The size of a cell 

 may be 1 -300th part of an inch in diameter ; some are larger, some 

 smaller ; the nucleus may be l-3000th of an inch in diameter ; the 

 nucleoli are 1-1 0,000th of an inch in diameter, more or less. 



The wall of a cell is chemically different from the nucleus ; for if 

 treated with dilute nitric acid, the wall is dissolved, and the nucleus 

 unaffected, so that we can in this manner isolate the nucleus. It is 

 not known whether there exists any chemical difference between the* 

 latter and the nucleolus ; and it is probable that the nucleolus is a 

 space in the nucleus containing a fluid. 



The elementary cell is imbedded in an amorphous matter, which is 

 termed cytoblastema, and is a fluid of greater or less consistence ; so 

 that in one case the cell may float, and in the other it may be im- 

 bedded. The matter between the cells is called intercellular substance. 

 Cells differ in their contents, which implies a difference in their walls, 

 inasmuch as they secrete the interior. 



The nucleolus was first discovered by Robert Brown in plants, and 

 its use made out by Schleiden. He discovered that the nucleus was 

 formed before the cell, and the latter was formed around it. After 

 this cells of different kinds were found in animals ; and Schwann 

 collected many instances, showing that animal and vegetable tissues 

 were developed from cells : this was an important generalisation. 



The mode of origin of the nucleated cell is this : cytoblastema first 

 exists ; in it is developed the nucleus, and around the latter is formed 

 the membrane of the cell from matters drawn from the cytoblastema. 

 The way in which the cell itself is formed is this : around a granule 

 we have a deposit forming a nucleolus ; round it again is formed the 

 nucleus ; a swelling of this membrane takes place, and is situated 

 over the others like a watch-glass, and thus the exterior cell is 

 formed. Coalescence of the granules forms a nucleus, and in the inter- 

 stices between these we find a fluid which is thought by Henle to form 

 the nucleoli. It has been observed, that a globule of oil in contact 

 with a small quantity of albumen drew from it a thin coating, which 

 enveloped the globule of oil ; and this albumen became coagulated, form- 

 ing a cell. When this globule was so surrounded, the coating became 

 wrinkled ; but when placed in contact with water it became distended, 

 thus proving it to be capable of endosmosis, or more probably an ab- 

 sorption of water by the wall of the cell, which consequently became 

 distended or swollen up, as there is no attraction between oil and 

 water. Nevertheless, elementary granules appear to be granules of 

 oil, surrounded by a covering of a protein compound. Milk globules., 



