134 ORGANS OF RESPIRATION. 



its origin. As much air as possible is now pumped with a 

 syringe out of the trachea, and the stop-cock closed. The 

 apparatus for injection having been previously put in readi- 

 ness, all must be connected, and the pressure raised in the tube 

 to the required point, i. e., sixty to eighty millimetres, so that 

 at any moment the stop-cock of the nozzle may be opened and 

 the injection begun. A sufficient quantity of cacao butter 

 having been fused in a capsule, a middle-sized syringe is filled 

 with the hot liquid, and fitted into the nozzle, which is inserted 

 into the trachea, and the injection begun* The moment that 

 the cacao butter has begun to enter, an assistant opens the 

 stop-cock 1 of the canula in the pulmonary artery. As soon as 

 the lung appears to be distended with the butter, the stop-cock 

 of the trachea is closed, but the injection of the bloodvessels 

 is continued. As soon as this appears to be complete, the left 

 auricle of the heart is comprised in a ligature, by tightening 

 which the pulmonary veins are completely closed. A few 

 moments later, the stop-cock in the artery is also closed, and 

 the animal placed in a basin so that the thoracic organs are 

 immersed in cold water. As soon as the lungs are seen to be 

 firm, they are taken out with the trachea and placed in common 

 alcohol. In two or three days, small portions may be cut out 

 and placed for a short time in absolute alcohol, and then 

 embedded for the preparation of sections. The sections must 

 be steeped in oil of turpentine or cloves, till the cacao butter 

 is dissolved out ; this may be ascertained by placing the watch- 

 glass containing them under a low power. Turpentine accom- 

 plishes this more quickly than oil of cloves. The sections 

 must be mounted in Dammar varnish. The relation between 

 the different bloodvessels and the capillary network of the 

 walls of the alveoli, are admirably seen in such preparations. 

 If it is intended to preserve the structure of the pulmonary 

 tissue unimpaired and at the same time to inject the blood- 

 vessels, half per cent, solution of salt or of bichromate of 

 potash may be substituted for the cacao butter, and two per 

 cent, solution of Prussian blue for the gelatin mass. The 

 organ must be placed in alcohol as before. 



1 Great care must be taken to keep the tube leading from the bottle 

 containing the mass, as well as the nozzle, warm with hot sponges, 

 otherwise there will be great danger of the solidification of the gelatin 

 in those parts, during the time which intervenes between the prepara- 

 tion of the apparatus and the commencement of the injection. 



