On Cell-wall Structure as seen in Cotton Hairs. 



431 



of any cell, equally with those of cotton hairs, are, after all, merely a special 

 case of the same procedure, while an analogy may be found in the medullary 

 rays of timber. 



Our partial elucidation of this structure has already thrown light on some 

 physical properties of the hair. Abnormal hairs are often found in which, to 

 a greater or less extent, the spiral structure is visible without any " develop- 

 ment." Our colleague, Mr. Slater, in the Physical Section of this Department, 

 has, in some preliminary studies, found the flexibility of such hairs to be- 

 highly abnormal, such hairs standing in the same relation to normal hairs, as 

 strands of yarn compared with solid wires of celluloid. We have mentioned 

 our opinion that the razor edge may produce molecular disturbances in the 

 cellulose. Akin to this is a remarkable phenomenon discovered by the junior 

 author, reminiscent of the results described by Griffith* with quartz rods. 

 If a hair has been pressure-treated to develop the pit spirals without re-agents 

 and then is subjected to stress in longitudinal extension, no alteration is 

 noticeable until the hair breaks ; after breaking, however, little or no trace 

 of the pit spirals is left in any part of the hair. We have failed to obliterate 

 the spiral cracks by any tension without actual breakage, and it would seem- 

 that, as in Griffith's work,f a molecular disturbance is needed, which the 

 back -lash of the break provides. 



Dimensions and Constitution of a Pit Spiral Fibril. 

 Taking - 4/z, as the thickness of a substantial growth-ring, and allowing 100 

 spirals to the ring in a hair whose original cell diameter was 15/z, and its. 

 mean wall diameter considerably less, gives us - 4/a square as the approximate 

 cross-sectional area of one Pit Spiral Fibril. Its length is apparently that of 

 the hair. Without undue speculation it is evident that we are here approaching 

 molecular dimensions, the probable size of the cellulose molecules being such 

 that some number of them between 1,000 and 100 would constitute the cross- 

 sectional area of one such pit spiral. There is even the slight possibility that 

 in these pit spiral fibrils we have reached the limits of morphology and are 

 examining a chemical (or colloido-chemical) unit. For other reasons, however, 

 we rather incline to the view that " cellulose," even in a pit spiral fibril, is a 

 complex of more than one kind of cellulose molecule. 



Origin of the Pit Spiral Structure. 



It seems clear to us that this secondary wall structure is a predetermined 



one, and that, paradoxically, we must therefore look to the period of growth 



* Griffith, A. A., " The Phenomena of Rupture and Flow in Solids," ' Phil. Trans.,' A, 

 vol. 221, p. 163 (1920). 

 t Griffith, loc. cit. 



VOL. XCIII. — B. 2 H 



