THE BIOLOGY OF THE CELL SURFACE 



bone. Studies on the development of fibres in connective 

 tissue, on that of cartilage and of bone indicate that these 

 structures which finally come to lie outside of the cell are 

 products of the ectoplasm. Indeed, it has been postulated 

 that connective tissue fibres even after deposition outside of 

 the cell are living ectoplasm. Whether living or not, the 

 intercellular substance of connective tissue and its deriva- 

 tives (cartilage and bone) are to be regarded as extreme 

 formations of ectoplasm, which have lost their organic 

 connections with their cells of origin. 



Intercellular fibres cast off hy cells are to be distinguished 

 from such fibres which are true cells, having nuclei. These, 

 muscle and some nerve cells, are characterised by their 

 great length and hence by a preponderance of surface to 

 mass. They thus possess relatively more living ectoplasm 

 as part of the cells than any other cells so far discussed. 

 Muscle-cells are notable for their high degree of contractility 

 and students of physiology regard this as a surface-phe- 

 nomenon. Fixed preparations of smooth or plain muscle- 

 cells (individual fibres) show longitudinal threads or fibrils 

 whilst striated muscle-fibres (both those of the heart and of 

 the skeletal or voluntary muscle) show in addition striations 

 running at right angles to the length of the fibres. Much 

 difference of opinion is expressed concerning the significance 

 of these fibrils because studies both on the developing and 

 the definitive muscle-fibres have yielded conflicting results 

 and led to various interpretations. In addition, many 

 investigators doubt the actual presence of fibrils in 

 muscle-fibres inasmuch as they have been unable to see 

 such in living cells. Although it would seem hazardous to 

 venture an opinion in view of this uncertainty with respect 

 both to the longitudinal threads described in fixed smooth 

 muscle and to the additional cross-striations reported in 

 striated (cardiac and skeletal) muscle as seen in fixed 

 preparations, nevertheless, I may offer suggestions concern- 



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