314 PROGRESS OF SCIENCE IN THE CENTURY. 



first he thought that, as the nucleus was the repro- 

 ductive organ of the cell, the secretion was formed in 

 the interior by the agency of the cell wall ; but three 

 years later he regarded it as a product of the nucleus. 

 The study of the process of spermatogenesis by his 

 brother, Harry Goodsir, in which the head of the 

 spermatozoon was found to correspond with the nu- 

 cleus 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." * This is in general 

 agreement with the modern conclusion that the nu- 

 cleus is the trophic centre of the cell. 



Following Verworn, one of the most enthusiastic 

 advocates and students of cell-physiology, we may 

 briefly indicate some of the paths of investigation 

 that have been pursued with success. 



(a) Unicellular organisms offer, as it were, a 

 natural analysis of the higher creatures. Types of 

 cell which occur in complex combinations in multi- 

 cellular organisms may be studied in isolation in 

 the unicellular forms. The study of their normal 

 behaviour has led to many interesting results, e.g., 

 as regards amoeboid movement and ciliary action. 



(h) Much has been done in the way of studying 

 the reactions of unicellular organisms to diverse arti- 

 'ficial stimuli of heat, light, and chemical re-agents, 

 as may be seen by a reference to the first two volumes 

 of Prof. Davenport's Physiological MorpJwlogy. 



(c) Microscopic vivisection-operations — to which 

 the most pronounced humanitarian can offer no ob- 

 jections, since there can be no question of pain nor 

 even of the destruction of life — have disclosed some 



* Sir William Turner, Pres, Address, Rep. Brit. Ass., 

 1900, p. 15. 



