50 PRACTICAL HISTOLOGY. 



DEVELOPMENT OF CAPILLARIES. 



The development of capillaries is easily studied in the tail of a half-grown tadpole prepared 

 by the ordinary gold chloride method. To see the capillaries distinctly it is well to remove 

 the superficial epithelium after staining. If the lemon-juice and gold method (p. xlv) be 

 employed, the formic acid employed afterwards removes the superficial epithelium. The 

 omentum of a new-born rabbit presents easily recognised whitish patches, or ' milk spots ' 

 (Ranvier) in it, which are aggregations of corpuscles like lymph-corpuscles ; and others, which 

 become continuous with buds given off from existing blood-vessels. These buds ultimately 

 become channelled to form blood-vessels. 



FRESH BLOOD-VESSELS. 



Take the pia mater, washed free from cerebral matter, and tease a small piece on a slide in 

 salt solution. Cover. An examination reveals the same general arrangement as described 

 above, but the nuclei of the muscular coat of the arteries requires the addition of acetic acid 

 to bring them into view. Add acetic acid, to observe this. It also swells up the adventitia, 

 makes it clear and transparent, and the elastic lamina when present, with its folds, is brought 

 clearly into view and so are the nuclei in the capillary wall. Do not preserve this. 



AORTA. 



PBEPABATION. Take small pieces of the human aorta or of the aorta of an ox, and 

 place it in picric acid for twenty-four hours. Make longitudinal and transverse sections in the 

 usual way, and stain them with picrocarmine, taking care not to wash the sections too much in 

 water, and mount them in Farrant's solution. 



EXAMINATION (L). Observe the fusion of the different coats and the large amount of 

 elastic fibres and plates in the different layers. All elastic tissue is stained yellow, connective 

 tissue pink, and non-striped muscle light reddish-brown, so that these different tissues are 

 easily distinguished (H). Note the numerous layers of elastic fibres in the inner coat ; in a 

 transverse section they appear as bright yellow granules ; in the longitudinal as yellow lines. 

 Note the large amount of elastic tissue in the middle coat, where it occurs in the form of 

 elastic laminae. 



If it be desired to see the lining epithelium, silver (p. xlv) the inner surface of the aorta of 

 an animal just killed, and mount a thin shaving in dammar. 



ISOLATED ELASTIC LAMINA. 



PREPABATION. By far the best method is the one I described several years ago for the 

 isolation of elastic tissue, viz., to digest thin strips of the aorta in artificial gastric juice 

 (p. 92) till everything except the elastic element is dissolved (De B. Birch). Wash the tissue, to 

 get rid of acid, and mount in Farrant's solution. Examination reveals all gradations, from 

 a network of elastic fibres to fenestrated membranes and sheets of elastic tissue. The elastic 

 fibres not unfrequently present transverse markings. 



