92 PRACTICAL HISTOLOGY. 



bottle is connected to a large air-chamber into which water can flow 

 from the water-tap, and thus compress the air. The pressure within 

 this cylinder can be registered by means of a manometer. The com- 

 pressed air acts on the surface of the injection mass in the Wolffs 

 bottle, and forces it through a tube which is attached to the cannula 

 fixed in the aorta. The large cylinder for the compressed air may be 

 made of tin, or one of the large stone jars used by spirit merchants, 

 or a carboy may be used. 



After the tissues are injected, they should be cooled rapidly by 

 being placed in running water. After the mass is completely set 

 the injected organs are cut into small pieces and hardened in 

 alcohol. 



The methods of interstitial injection of fluids and the puncture 

 methods are referred to in the text. 



XVI. EXAMINATION OF FRESH TISSUES AND 



FLUIDS. 



In examining a fresh tissue or organ snip off a small part with 

 scissors and tease it in normal saline, or one of the indifferent fluids 

 mentioned in Chapter III. A convenient plan with some organs, 

 e.f/. t lymphatic gland or liver, is to make a fresh cut and scrape 

 the surface with the blade of knife, and then examine the scrapings. 



If it be desired to study the tissue elements, it may be placed in 

 one of the macerating media mentioned in Chapter IV., the parti- 

 cular fluid selected depending, of course, on what object is sought 

 to be obtained. 



If it be desired to render certain parts of the tissue more trans- 

 parent, it may be examined in glycerine. 



Again acetic acid (1-2 per cent.) may be added to a fresh tissue. 

 It has the double action of making connective tissue swell up 

 and become transparent, thus making nuclei more evident, while it 

 also shrivels the latter somewhat. Albuminous granules are dis- 

 solved by it, while oil globules are not, so that it may be useful 

 occasionally in determining the nature of the granules in proto- 

 plasm. Elastic fibres are not affected by it, and thus can readily 

 be distinguished from the white fibres of connective tissue. Groups 

 of micro-cocci are also not affected by it. 



The tissue may be stained by acetic fuchsin. This is made as 

 follows : To a 2 per cent, solution of acetic acid add sufficient 

 fuchsin to give a saturated red colour (Kahlden). This reagent not 

 only makes the nuclei visible, but it stains them as well. 



Sometimes a weak watery solution of iodine makes the outlines of 



