ELECTRON ^IK.KOSCOPY 



^S/* 



Fig. 6. Cowhide collagen fibrils. 52,500X • Same 

 as Figure 5. 



due to the fact that the electron-dense chro- 

 mium complex deposited on the plastic film 

 supporting the collagen fibrils, especially 

 along the edges of the fibrils, acts as a dark 

 background for the light fibrils. 



Figures 5 and 6 show collagen treated with 

 lead nitrate. These are examples of pseudo- 

 electron staining as explained in the text 

 above. 



REFERENCES 



1. BoRASKY, R., J. Am. Leath. Chem. Assoc, 52, 



596-610 (1957). 



2. Hall, C. E., /. Biochem. Biophys. Cytol. 1, 1 



(1955). 



3. MuDD, S., AND Anderson, T. F., J. Expt. Med., 



76, 103-108 (1942). 



4. Porter, K. R., and Kallman, F., Exp. Cell. 



Res., 4, 127 (1953). 



5. Symposium on Electron Staining, J . Roy. 



Micro. Soc, Series III, 78, Parts 1 and 2 

 (1959). 



6. Watson, M. L., /. Biochem. Biophys. Cytol., 3, 



1017 (1957). 



R. BoRASKY 



TISSUES (CONNECTIVE), BONES AND TEETH 



Apart from cancer, most of the non-infec- 

 tious maladies from which the human race 

 suffers are related to changes in the structure 

 or function of the connective or hard tissues. 

 The primary aim of the work which has so 

 far been done on this group of tissues has 

 been to establish a clear picture of their 



normal appearance to compare with similar 

 preparations of pathological specimens. 

 These tissues, which form the framework of 

 the body, consist mostly of a matrix of long 

 chain polymeric compounds with which their 

 formative cellular elements are associated. 

 In bones and teeth the matrix is made rigid 

 by the deposition of calcium salts. Strictly 

 speaking, the connective and hard tissues 

 are mesodermal in origin, and consist of 

 fibrous proteins embedded in a polysaccha- 

 ride-containing medium. Two ectodermal 

 structures will also be considered in this 

 chapter: tonofibrils, which have as their 

 main function the holding of the epidermis 

 together; and dental enamel, which fits 

 naturally into the group of hard tissues. 



Collagen and polysaccharide-containing 

 ground substance are universal in the animal 

 kingdom. Leech connective tissue and devel- 

 oping human connective tissue have fibro- 

 blasts and collagen which look identical; 

 while in teeth one has to get as far away from 

 the human as a sea urchin to find calcium 

 salts which are not predominantly hydroxy- 

 apatite. On the other hand, there are minor 

 differences in many closely related species. 

 Thus, some details in the development and 

 calcification of the epiphyseal cartilage of 

 the rat and rabbit, both rodents, show differ- 

 ent appearances. 



In any study of tissue structure the great- 

 est amount of information is obtained when 

 the electron microscopic appearance is con- 

 sidered in conjunction with findings from 

 other methods. It has not superseded other 

 established techniques, the most important 

 of which is still the light microscope. Some- 

 times it is sufficient for the electron micro- 

 scope to fill in details after the greater part 

 of the work has been done using light micro- 

 scope techniques, involving staining, as in 

 the detailed investigation of the growth of 

 epiphyseal cartilage. At other times, the 

 most important part of the investigation is 

 done using the electron microscope, as in the 

 sorting out of the mechanism of dental caries. 



276 



