ELKCTHON MICKOSCOl'Y 



of different sites. The collagen fibrils formed 

 by a single fibroblast appear to be tubular 

 and of more or less uniform diameter. 



Collagen fibrils laid down away from cells 



Fig. 5. Fibroblast from 6 week regenerating 

 tendon. Fixed with osmium tetroxide and stained 

 with P.T.A. Embedded in araldite. X10,000. 

 Photograph bj^ J. A. Chapman and R. Peach, 

 Manchester University. 



tend to have a different appearance. Often 

 they are very fine, as in the collagen from 

 epiphy.seal growth cartilage (Fig. 10), and 

 separated from the cells by an even finer 

 mesh of ground substance. A much larger 

 range of fiber diameters is also frequent. In 

 Fig. 14, from a specimen of normal adult ar- 

 ticular cartilage, a collagen fiber of very large 

 diameter is seen in the plane of the section. 

 Elastin. Many papers have been written 

 on the electron micro.scopy of elastin, and 

 much confusing and contradictory informa- 

 tion offered. There is now, however, a meas- 

 ure of agreement. R. W. Cox (Thesis, Oxford 

 1957) has carefully compared the appearance 

 in the electron microscope with alternate 

 sections stained and prepared for light mi- 

 croscope examination. He has also isolated 

 it chemically. When wet it has rubber-hke 

 elasticity; when dry it is brittle. Elastin is 

 found in those tissues where a quick recovery 

 from applied stresses is necessary, and there 

 is some evidence to suggest that it is pol- 

 ymerized in situ, rather than being precipi- 

 tated in a manner analogous to collagen. Its 

 form and size can be very irregular, and in 

 the electron microscope the safest method 

 of identification is to examine the texture in 



Fig. 6. Fibroblast from dog intervertebral disc. Delayed fixation with formalin. The cytoplasm is 

 degraded, thus showing that no collagen fibrils have penetrated to cell wall. Part of this wall is ex- 

 panded as compared with the rest. Embedding medium removed. Stereoscopic photograph. 



280 



