THE BIOLOGY OF THE CELL SURFACE 



These manifestations definitely coincide with the break- 

 down of material in the ectoplasm and with the rapid recon- 

 stitution whereby the egg-surface builds itself anew. They 

 are fundamental physiological expressions of vital activity 

 and have their cause in the visible structural changes at the 

 egg-surface which have been observed both on the normal 

 e^g and on that exposed to the action of dilute sea-water. 

 Sperm-attachment is for the unfertilized egg the normal 

 and best means of stimulation; as a stimulus the sperma- 

 tozoon calls forth the same responses in the egg — oxygen- 

 consumption, conduction and contraction — elicited by 

 stimuli acting on other cells. This similarity I hold to be 

 of fundamental significance for cell-physiology for I con- 

 ceive these modes of response to be properties of the ecto- 

 plasm of cells generally. The grounds for this conception 

 follow. 



Few investigators to-day support the old theory of the 

 nucleus as the seat of cellular oxidation. The human red 

 blood corpuscle is pre-eminantly an oxygen-carrier; it has 

 no nucleus. If there be evidence of increased accumulation 

 of oxygen in the region of the nucleus of a cell, this more 

 likely is caused by the presence of the nuclear membrane 

 rather than by nuclear substance. Positive evidence indi- 

 cates that oxygen-consumption depends upon cell-struc- 

 tures, that is, upon minute surfaces in the protoplasm; even 

 triturated cells consume oxygen.^ Then the cell surface 

 constitutes, par excellence, an oxygen-uptaking structure. 

 And since this surface is subdivided into processes and its 

 area therefore increased many times, its effectiveness is 

 enhanced. In higher organisms, as the vertebrates, the 

 cells which take up oxygen are rich in surface — as cells of 

 the gills in aquatic and of the lungs in terrestrial animals. ^ 



1 Warburg, 1914. 



- The entire inner surface of a 7nan's lungs aviounts to about 

 go square meters, more than 100 times the area of the skin. 



118 



