X-RAY MICROSCOPY 



induce high x-ray absorption (thyroid). 

 Most animal tissues are formed from ele- 

 ments of low atomic number, but curious 

 and often inexplicable variations in cellular 

 radiodensity occur. The chemical significance 

 and interpretation of these microscopic areas 

 of transparency and selective absorption 

 await study. 



Freeze drying and substitution have been 

 found to give the best tissue fixation for 

 x-ray microscop3% as well as the best con- 

 trast, since they produce few or no chemical 

 changes and remove only water. Also, as in 

 optical microscopy (3) , it has been confirmed 

 that flotation of tissue sections causes cyto- 

 logical changes and solution losses, and that 

 both structural and density differences are 

 readily detectable in comparison x-ray mi- 

 crographs taken of serial sections after they 

 have been either dry -mounted or floated out 

 over water or safine (4). The latter may 

 yield better pictures but are not representa- 



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Fig. 1. X-ray micrograph of human sebaceous 

 gland showing the cell boundaries and dark radio- 

 lucent lipid droplets within the cells. Part of a hair 

 follicle is also seen. Mag. X375 



tive of the tissue, and hence this point must 

 also be considered in carrying out x-ray 

 absorption analyses of tissue. 



Unstained sections of animal and human 

 tissues, both soft and mineralized, can be 

 studied by x-ray projection microscopy, such 

 as skin, hair, sebaceous gland, kidney, sub- 

 maxillary gland, cartilage and bone. Micro- 

 graphs of human skin clearly show the cells 

 and intercellular boundaries of the stratified 

 epidermis, and also the keratinized strands 

 at the skin surface. The structure of hair and 

 its appendages can be well visuahzed by 

 projection microscopy owing to the presence 

 of hard and soft keratin, both of which con- 

 tain sulfur. Cross sections of human scalp 

 show, for example, the process of keratiniza- 

 tion among the cells of the inner root sheath 

 of the hair follicle, and such details as the 

 polygonal cells and stratum cylindricum of 

 the outer root sheath of the hair follicle. 

 The accumulation of lipid droplets within 

 the cells of hmnan sebaceous glands is strik- 

 ingly recorded, appearing as dark radiolucent 

 spherules which contrast markedly with the 

 white x-ray absorbent cell membranes and 

 cell nuclei (Fig. 1). Other micrographs show 

 the manner in which the lipid droplets 

 coalesce, forming a uniformly black cyto- 

 plasm about the white "doughnut-like" nu- 

 cleus just before the mature cells break 

 down. 



Many of the differences Avhich occur in 

 glandular epithelium from organ to organ 

 and within the same organ can be detected 

 by x-ray microscopy. For example, projec- 

 tion micrographs of the submaxillary gland 

 show terminal ramifications and cytoplasmic 

 differences, such as the conglomerate appear- 

 ance of the acinar cells and peculiar radio- 

 lucency of the cells of the granular tubules. 

 Other features visible are the striations of 

 the intralobular salivary ducts, epithelium 

 and basement membrane of the intercalated 

 ducts (Fig. 2). Projection micrographs of 

 human foetal tissue such as the developing 

 thyroid gland yield interesting details such 



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