108 STUDENTS HISTOLOGY 



thoracic lymphatic cavities are, perhaps, the most convenient and 

 typical for demonstration. 



LYMPHATIC VESSELS OF THE CENTRAL TENDON OF THE 

 DIAPHRAGM (Figs. 76 and 77) 



Practical Demonstration 



This demonstration should be made with tissue from the rabbit, inas- 

 much as the slightest decomposition of the endothelium would be fatal to 

 success. 



A small (preferably white) rabbit should be quickly killed by decapitation, 

 and immediately suspended by the hind legs, so as to thoroughly drain the 

 body of blood. As soon as the blood has ceased dripping, open the thoracic 

 cavity by slitting up the skin along the median line, pushing it to the sides 

 and removing the sternum. In this operation work rapidly and avoid soiling 

 the internal parts. Then with the fingers of one hand raise the lungs and 

 heart from the diaphragm, and with a large camel's-hair brush proceed to 

 quickly, and quite forcibly, pencil the white, glistening surface of the central 

 diaphragmatic tendon, moistening the brush from time to time in the lymph 

 of the pleural cavity. Should the quantity of fluid be small, add a little dis- 

 tilled or previously boiled and filtered water. The object of the brushing is 

 to remove the endothelial cells which cover the surface, and which would 

 otherwise hide the lymph-spaces. After the penciling, drain away the fluid 

 and pour over the brushed surface a one -fifth per cent, .solution of nitrate of 

 silver.* Allow the silver solution to remain for twenty minutes in contact 

 with the tissue, the body meanwhile being kept away from the bright sunlight; 

 then pour off the solution, wash the surface twice with distilled water, and 

 afterward allow water from the tap to flow over the parts for at least five 

 minutes. 



If you observe the directions carefully, the surface of the tendon will lose 

 its original glistening appearance and become whitish and opaque. 



The tendon, or such portion of it as you wish to preserve, may be cut out 

 with the scissors after the washing, thrown into glycerin, and placed in the 

 sunlight until the surface becomes brown. With the forceps tear off small 

 pieces of the stained side, say one -half inch square, and examine in glycerin, 

 or mount them permanently in the same medium. 



The demonstration of the channels of the lymphatic system is 

 based upon the following : 



1^ Lymph -channels are always, however small or irregular, 

 lined wiih flattened cells in a single layer i. e., endothelium. 



2. The lining cells are cemented together with an albuminous 

 substance. 



3. Nitrate of silver combines ivith the cement, forming albumi- 

 nate of silver, which becomes dark brown when exposed to light. 



* Water which has been well boiled in a clean vessel, and afterward carefully filtered, may 

 generally be employed in histological work when distilled water is not available. 



