72 



the ventricle and note a small band of connective tissue pass- 

 ing from its dorsal surface to the adjoining- wall of the peri- 

 cardium. Seize this band with the forceps and divide it 

 between the forceps and the pericardial wall. Connect the 

 apex of the ventricle with a heart lever and take a tracing of 

 the heart beat upon the kymograph (revolving- drum). Paste 

 the tracing in your notes. Lift up the apex of the ventricle, 

 by means of the band already described, and with a sharp 

 pair of scissors cut through the right and left aortae, the pre 

 and post caval veins, and the surrounding tissue, taking care 

 not to injure the sinus venosus. Place the heart in a watch- 

 glass, moistening occasionally with normal saline solution. ^ 

 The beats will not be interrupted at all, or for a very short 

 time only. 



272. Watch the beating of the heart. Do the auricles 

 and ventricle contract simultaneously? What are the number 

 of beats per minute ? Compare with 271. 



273. Lift up the apex of the ventricle, and with the 

 scissors cut off the apex at the upper third of the ventricle. 

 Watch the separated portions. Is there any difference in the 

 beating ? 



274. With the scissors separate the two auricles from 

 each other, letting the attached portion of the ventricle 

 remain to each auricle. Do they continue to beat ? 



275. The same frog, if it has been kept in a moist place, 

 may be used for the following cilia experiment : Place the 

 frog upon its back, and cut through the lower jaw, along the 

 midline, continuing the incision down the oesophagus as far 

 as the stomach. Pin the parts back and moisten the mucosa 

 with normal salt solution, if it is at all dry. Place a small, 

 thin piece of cork upon the mucosa just below the orbits, and 

 note that the cork is carried toward the stomach by the cilia. 

 Warm a little of the normal salt solution to 30° C, and repeat 

 the experiment. Apply heavier bits of substance to the 

 mucosa, and note if their positions are changed. Apply to 

 the strip of mucosa a few drops of a saturated solution of 

 chloretone and note whether the motion of the cilia is affected 

 or not. With a scalpel scrape some of the mucosa and exam- 

 ine the ciliated cells in saline solution under the microscope. 



iMade by dissolving 6.5 grams of sodium chloride in one liter of distilled 

 water. 



