XIX.] THE HEART AND BLOOD-VESSELS. 233 



If desired, the phenomena of inflammation can readily be 

 studied by applying some irritant to the web, e.y. t mustard or 

 creosote (one minute). 



ADDITIONAL EXERCISES. 



13. Elastic Fibres in Arteries (Martinotti). Harden the blood-vessel in 

 chromic acid, make sections, and stain them with safranin as directed in 

 Lesson X. 10. All the elastic fibres are purplish or black. Herxheimer's 

 Method (p. 161) also yields good results. 



14. Development of Blood- Vessels. (i.) Harden the omentum of a newly- 

 born rabbit in Flemming's fluid for twenty-four hours. Wash it thoroughly to 

 remove all the hardening solution, Stain a piece for 24-36 hours in safranin. 

 Remove the surplus stain in the usual way with acid alcohol. Mount in 

 balsam. 



(ii. ) Kill a rabbit five days old with chloroform ; do not bleed it. Open 

 the abdomen, remove the stomach and spleen, and attached to them the 

 omentum. Place all in a saturated 

 watery solution of picric acid for one 

 hour ; wash away all the picric acid, cut 

 out a small piece, stain it in logwood and 

 then with eosin, or double stain it at 

 once in eosin-hsematoxylin. Mount in 

 Farrant's solution. 



(a.) (H) Search for a network of capil- 

 laries, which is easily found. Try to 

 find one of them which gives off a long, 

 narrow, blunt process. The process may 

 be found partially channelled (hg. 22l). a Ne w-Born Rabbit. Flemmiug's 



By the union of two such processes, which fluid and safranin. 



ultimately become hollow, new capillary 



arches are formed. The blood-corpuscles in a preparation of (ii.) are stained 

 with eosin. 



15. Nerves and Nerve-Cells in a Frog's Heart. Pith a frog, expose its 

 heart, cut away the pericardium, divide the frjenuin. which connects the pos- 

 terior surface of the ventricle to the pericardium ; raise the heart, find the 

 sinus venosus, ligature the inferior and two superior vense cavae which open 

 into the latter, make an incision into otie of the aortae, and into it tie a fine 

 glass cannula. Inject normal saline so as to wash out the cavities of the 

 heart. Distend the heart-cavities with the following mixture : Four parts 

 of gold chloride (2 per cent.) and one of formic acid boiled together and 

 allowed to cool. Ligature the other aorta, so as to get the heart-cavities fully 

 distended. Place a ligature below the cannula, cut out the heart and place it 

 for ^-i hour in 5 cc. of the gold mixture. Open the auricles, wash out the 

 heart in water, and expose it to light in distilled water 50 cc. containing 

 three drops of acetic acid. Reduction of the gold takes place slowly in 3-4 

 days. Cut out the auricular septum and examine it in glycerine. 



Pyriform nerve-cells, each with a straight and a spiral process, will be 

 found along the course of the nerves in and near the auricular septum. 



The nerve-fibres in the auricular septum are readily found by using instead 

 of the gold a. 2 per cent, solution of osmic acid. 



The Methylene-blue method yields excellent results, if the fresh auricular 



