200 PRACTICAL HISTOLOGY. 



I 



we make use of the nitrate of silver, but the mode 

 of proceeding is somewhat different from that ordi- 

 narily employed. A gelatine mixture is made by 

 taking ten grammes of gelatine, and, after soaking 

 it in cold distilled water, melting it, and adding if 

 necessary more warm distilled water until the mix- 

 ture measures 100 c.c. A decigramme of nitrate of 

 silver is dissolved in a little distilled water and 

 added to the gelatine, and the mixture is transferred 

 to a glass syringe, which is kept warm over a water- 

 bath. An animal preferably a young one having 

 been killed, the lungs are removed, a glass canula 

 with a small piece of India-rubber tube attached is 

 tied into the trachea, and then the point of the 

 syringe is slipped into the open end of the India- 

 rubber tube, and enough of the gelatine mixture 

 injected into the lungs to distend them pretty com- 

 pletely. The trachea is now tied and the canula 

 removed from it. The lungs are then put aside into 

 a cold place until the gelatine within them has fully 

 set, when sections, which should be as thin as possi- 

 ble, are made with a razor, either not wetted at all 

 or with distilled water only. The sections so ob- 

 tained are placed on a slide in glycerine, covered, 

 and exposed to the light. As soon as they seem 

 sufficiently stained they may be examined with as 

 high a power as possible, for the purpose of making 

 out the silver lines between the epithelium cells. 



Preparation 7. Bloodvessels of the lungs. 

 Lastly, the pulmonary vessels are to be injected and 

 sections made of the injected lung. The red gela- 

 tine injection may be used ; this and everything else 

 is to be got ready just in the same way as for the 

 injection of the aortic system, but a syringe filled 

 with melted cacao-butter must be connected with 

 the trachea in the same way as for the gelatine mix- 

 ture in the last paragraph ; and moreover the arte- 

 rial canula is of course to be passed through tlie 

 right ventricle and tied into the pulmonary artery, 

 instead of into the aorta. Immediately the gelatine 



