302 



M. W. ANDREWS AND J. SIKORSKI 



ever, the cortical cells isolated from untreated keratin 

 by mild digestion in trypsin (3) appeared to be little 

 affected by the prolonged action of ultrasonic vibra- 

 tions (25 Kc/s and 15 Watt/cm-, actual output) in 

 water or various swelling agents: the separated 

 fragments showed very little internal structure (6). 

 It was thus advisable to increase the time of treat- 

 ment in trypsin to obtain better retting effects. 



The experiments were carried out with non-medullated 

 root-ends of Australian merino and Lincoln wool fibres. 

 These were cleaned by extraction in petroleum ether at 

 room temperature for about a week, followed by Soxhiet 

 extraction first in benzene and then in ethyl alcohol 

 for 24 hours. The fibres were washed in repeated changes 

 of distilled water to remove water-soluble impurities and 

 then dried at room temperature. 



Fibres were then treated in a mixture, containing equal 

 proportions of 0.5"o w/v aqueous solution of trypsin and 

 a buffer solution of pH 8.6, at 40 C, using a wool to solu- 

 tion ratio of 1 :100. After three months both samples of 

 wool retained their fibrous form, but on pressing gently 

 between a microscope slide and a cover slip, they yielded 

 cortical and cuticular cells; the latter were separated using 

 Woods' technique (15). The purified cortical cells were 

 kept (in a stoppered flask) in distilled water to which a 

 drop of toluol had been added to prevent bacterial 

 growth. 



Small samples of cortical cells were suspended in dis- 

 tilled water, or lithium bromide solutions', in a cell of an 

 ultrasonic apparatus (5) and were irradiated for periods 

 up to 12 hours. 



The cortical cells isolated from Australian merino 

 wool and irradiated by ultrasonic vibrations in 

 water suspensions, appeared to break into large 

 aggregates of the parallel macrofibrils, in agreement 

 with the view that a macrofibrillar type of structure 

 is characteristic in this type of keratin (see fig. 1). 

 When, however, similar experiments were made 

 with the cortical cells separated from Lincoln wool, 

 their breakdown in water suspensions started with 

 the separation of many superimposed layers (up to 

 eight) of the sheets of microfibrils (see fig. 2). Some 

 seemingly structureless material was found to be 

 situated between these sheets (7); such films could 

 often be seen over the cracks in the sheets of micro- 

 fibrils (see fig. 2). 



In agreement, however, with our previous experi- 

 ence with the chemically untreated keratin (6), we 

 found it impossible to separate the very thin sheets 

 of microfibrils from their thicker aggregates. 



The discrete steps of breakdown could, however, 

 be obtained when the cortical cells, isolated from 

 Lincoln wool, were subsequently exposed to the 

 action of ultrasonic vibrations in lithium bromide 

 solutions (fig. 3). During these experiments we have 

 obtained evidence of the separation of many thin 

 sheets of the microfibrils "peeling off" from the out- 

 side surfaces of the cortical cells, even after relatively 

 short time of treatment (four hours). We have also 

 observed that some less resistant cells were disinte- 

 grating into the thin sheets of microfibrils and the 

 residues of some globular material could be seen 

 scattered over their surfaces (see fig. 4). 



C C M 



■MIF" Type 2 



C.C M 



■■MIF" Type 2 



Fig. 5. Diagram illustrating cortical ceil. MIF, microfibril; 

 MACF, macrofibril; C.C.M., cortical cell membrane. 



The results of our experiments indicate that the 

 differences in stability of the cortical cells to the 

 action of ultrasonic vibrations are not confined to 

 crimpy wools only. 



The most resistant cortical cells isolated from the 

 other (uncrimped) wool remain unaffected by the 

 action of ultrasonic vibrations for considerable pe- 

 riods of time. The less resistant cells show the sepa- 

 ration of thin sheets of microfibrils, followed by the 

 appearance of aggregates of the microfibrils. The 

 presence of small debris (other than that of the 

 intercellular origin) in the early stages of treatment 

 of cortical cells suggests that there are also some 

 cells of very low stability. 



Thus, there is no doubt that a considerable diffe- 

 rentiation does exist in the organization of cortical 

 cells, and we suggest that the following model (see 

 fig. 5) could account for the available evidence. We 

 suggest that the cortical cells are surrounded by a 

 relatively high number of thin sheets of microfibrils 

 and that there is also some less orderly arrangement 

 of the aggregates of microfibrils inside the cortical 

 cells; consequently we agree that the idea of the 

 existence of the macrofibrillar structure in the interior 

 of cortical cells should be regarded as consistent 

 with the experimental evidence. 



The idea of the extensive sheets of microfibrils has 

 been very recently supported by some x-ray evidence 

 kindly placed at our disposal by Mr. Woods and 



1 The lithium bromide solutions used in experiments de- 

 scribed in this paper, were made by dissolving 100 g of salt 

 in 100 ml of distilled water. 



