386 



SCIENCE. 



[N. S. Vol. XII. No. 298. 



nucleus. The study of the process of sper- 

 matogenesis by his brother, Hany Good- 

 sir, in which the head of the spermatozoon 

 was found to correspond with the nucleus 

 of the cell in which the spermatozoon arose, 

 gave support to the view that the nucleus 

 played an important part in the genesis 

 of the characteristic product of the gland 

 cell. 



The physiological activity of the cell 

 plasm and its complex chemical constitution 

 soon after began to be recognized. Some 

 years before Max Schultze had published 

 his memoirs on the characters of proto- 

 plasm, Briicke had shown that the well- 

 known changes in tint in the skin of the 

 Chamseleon were due to pigment granules 

 situated in cells in the skin which were 

 sometimes diffused throughout the cells, 

 at others concentrated in the center. Sim- 

 ilar observations on the skin of the frog 

 were made in 1854 by von Wittich and 

 Harless. The movements were regarded as 

 due to contraction of the cell wall on its 

 contents. In a most interesting paper on 

 the pigmentary system in the frog, pub- 

 lished ia 1858, Lord Lister demonstrated 

 that the pigment granules moved in the 

 cell plasma, by forces resident within the 

 cell itself, acting under the influence of an 

 external stimulant, and not by a contrac- 

 tility of the wall. Under some conditions 

 the pigment was attracted to the center of 

 the cell, when the skin became pale ; under 

 other conditions the pigment was diffused 

 throughout the body and the branches of 

 the cell, and gave to the skin a dark color. 

 It was also experimentally shown that a 

 potent influence over these movements was 

 exercised by the nervous system. 



The study of the cells of glands engaged 

 in secretion, even when the secretion is 

 colorless, and the comparison of their ap- 

 pearance when secretion is going on with 

 that seen when the cells are at rest, have 

 shown that the cell plasm is much more 



granular and opaque, and contains larger 

 particles during activity than when the cell 

 is passive ; the body of the cell swells out 

 from an increase in the contents of its 

 plasm, and chemical changes accompany 

 the act of secretion. Ample evidence, 

 therefore, is at hand to support the position 

 taken by John Goodsir, nearlj' sixty years 

 ago, that secretions are formed within 

 cells, and lie in that part of the cell which 

 we now say consists of the cell plasm ; that 

 each secreting cell is endowed with its own 

 peculiar property, according to the organ in 

 which it is situated, so that bile is formed 

 by the cells in the liver, milk by those in 

 the mamma, and so on. 



Intimately associated with the process of 

 secretion is that of nutrition. As the cell 

 plasm lies at the periphery of a cell, and 

 as it is, alike both in secretion and nutri- 

 tion, brought into closest relation with the 

 surrounding medium, from which the pabu- 

 lum is derived, it is necessarily associated 

 with nutritive activity. Its position en- 

 ables it to absorb nutritive material di- 

 rectly from without, and in the process of 

 growth it increases in amount by intersti- 

 tial changes and additions throughout its 

 substance, and not by mere accretions on 

 its surface. 



Hitherto I have spoken of the cell as a 

 unit, independent of its neighbors as re- 

 gards its nutrition and the other functions 

 which it has to discharge. The question 

 has, however, been discussed, whether in a 

 tissue composed of cells closely packed 

 together cell plasm may not give origin to 

 processes or threads which are in contact 

 or continuous with corresponding proc- 

 esses of adjoining cells, and that cells may 

 therefore, to some extent, lose their indi- 

 viduality in the colony of which they are 

 members. Appearances were recognized 

 between 1863 and 1870 by Schron and 

 others in the deeper cells of the epidermis 

 and of some mucous membranes which 



