156 



M. S. C. BIRBECK AND E. H. MERCER 



narrow intercellular cleft between these two masses 

 of cytoplasm, which appears circular or ovoid in 

 cross section, very often contained numerous col- 

 loidal particles within 2 minutes following injection. 

 Since the discovery that very dilute colloidal vital 

 dyes are segregated in highly concentrated spherical 

 inclusions by phagocytes, there has been much specu- 

 lation concerning the manner in which these inclu- 

 sions are formed. It is now possible with the electron 

 microscope to follow the progress of colloidal parti- 

 cles as they enter the phagocyte, and thus gain a 

 clearer idea of the mechanism involved. Though the 

 present study is far from complete, it indicates that 

 particles enter the phagocyte in spheroidal and in 



cleft-like depressions of the cell membrane that 

 secondarily pinch off from the cell surface to form 

 intracellular inclusions. The clefts, whether they pre- 

 exist or form by invagination in response to the 

 presence of particles, appear to represent the more 

 important form of phagocytosis mechanism (fig. 2). 



References 



1. Parks, H., Amir. Rec. 125, 1-16 (1956). 



2. — These Proceedings, p. 152. 



3. Parks, H., Peachey, L., and Chiquoine, A., Auat. Rec. 



124 (1956) (Abstracts of meetings of American As- 

 sociation of Anatomists). 



The Role of Cell Membranes in Morphogenesis 

 M. S. C. BiRBECK and E. H. Mercer 



Chester Beatty Research Institute of Cancer Research: Royal Cancer Hospital, London S. W. 3 



The study of morphogenesis by electron microscopy 

 is likely to prove a formidable undertaking. However, 

 the labour can be lessened by the choice of an appro- 

 priate system in which there are present not only 

 various examples of differentiated cells but, at the 

 same time, cells in different stages of development. 

 It is a further advantage to have the different stages 

 distributed in the tissue in an easily recognised man- 

 ner. 



Systems of cells satisfying these demands are not 

 common. One, which is admirable for the purpose, 

 is the follicle of the growing hair of the mammalian 

 skin. Here we find at the end of a small tube, the 

 outer root sheath, dipping down into the skin, a 

 germinal matrix producing a steady stream of cells 

 which, passing along the tube, differentiates into 

 the six concentric cylinders of cells which form the 

 hair and its enveloping sheaths. In the distance of a 

 few 100 fi of the tube we find cells in the following 

 stages: dividing cells, undifferentiated cells, cells in 

 early differentiation and differentiated cells engaged 

 in synthesis of their characteristic products. It is 

 thus possible in a single electron microscopic section 

 to find examples of cells in all stages of their devel- 

 opment arranged in a linear sequence. 



Taking advantage of this situation, we have ex- 

 amined in hair foUicles^fixed, embedded and sec- 

 tioned by the now standard procedures — the events 

 associated with early differentiation, which occur in 

 the mid and upper regions of the bulb (see figure 1). 

 By comparing the cells of the undifferentiated matrix 

 with those, a few cell diameters further along the 

 follicle which show definite signs of differentiation, 

 we have been led to suspect that the contacts between 

 the surfaces of the cells play a leading role in mor- 

 phogenesis. (See also reviews (5) and (6).) 



PRE-KERATINOUS 

 ZONE 



CONSTRICTION 

 ZONE 



Fig. 1. Diagrammatic representation of the behaviour of 

 cell membranes and morphogenetic developments in the 

 hair follicle with reference to the hair cuticle. In the outline 

 of the follicle, shown in the centre, the changes in the cu- 

 ticular formation and the several zones of the follicle are 

 indicated. On the L.H.S. is shown a series of cells (A to D) 

 in which cell contacts are shown developing, spreading and 

 deforming the cells. 



