THE ECTOPLASM 



The cylindrical cells of the human intestine, measuring 

 22-26 by 6 At, show on the side presented to the intestinal 

 lumen a brush border or bordure en hrosse. Thus, in these 

 cells as in those of the kidney and liver one notes an ecto- 

 endoplasmic differentiation. 



In the skin are cells which interlock by means of fine 

 threads, the so-called intercellular bridges.^ Cells of other 

 tissues are connected similarly, as for example those in the 

 retina of the eye. Though many claim that these connec- 

 tions are artefacts, the abundance of evidence from studies 

 on various tissues from many different animals supports the 

 view that these connections are normal cell-processes. As 

 such they are evidence of ecto-endoplasmic differentiation. - 



In view of the substantial body of convincing data 

 showing the presence of intercellular connections, it 

 becomes difficult to understand why many authors still deny 

 their existence and assert that fixation creates them. But 

 quite apart from the demonstration of these intercellular 

 connections in well-fixed tissues exist clear cases, some of 

 them among the earliest described, showing living cells in 

 rich connections with each other. As will be shown later 

 connections between cells of the developing egg have 

 been long known and can be easily demonstrated. I think 

 that almost no one to-day doubts that in the nerve-system 

 the neurones are in contact with each other by processes 

 which make the synaptic membranes. 



The body-structure of higher animals, especially of 

 vertebrates including man, embraces certain groups of cells 

 notable for the presence of extra-cellular substances asso- 

 ciated with and produced by them. These groups of cells 

 comprise the binding or connective tissues of the body. 

 Their products are fibres of various kinds, cartilage and 



^ See Schuberg, IQOJ^ and later -writers. 

 - Flemniing, /t?79, on living cells. ' 



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