60 



EXERCISE VIII 



ANNOTATION 



Ohs. 37. Eupturing a cusp of the aortic 

 valve bears on a common variety of heart 

 disease where the valve, owing to changes in 

 its texture or actual loss of its substance, fails 

 to close properly. A characteristic symptom 

 of such valvular disease is the abnormal 

 increase of the oscillations of the arterial pulse 

 (Hodgkin, Lond. Med. Gazette, iii, 433,1829; 

 Corrigan, Edinh. Med. and Surg. Joiirn., 

 xxxvii, 225, 1832). The increased oscillation 

 is due to an abnormally low diastolic arterial 

 pressure, while the systolic is little less than, 

 sometimes even above, normal. With a 

 little care, the inertia of the membrane 

 manometer and fluid junctions can be kept 

 within limits not too great to follow fairly 

 the oscillations of the pulse. Even with the 

 Hg manometer the increased pulse oscilla- 

 tions can be seen, and the Hg manometer 

 shows perhaps more clearly than do most 

 pulse-recorders the compensatory adjustment 

 on the part of the heart. This compensation 

 maintains, or nearly so, the mean arterial 

 pressure, despite the diastolic leakage of blood 

 back into the ventricle after its delivery into 

 the aorta at systole. 



Experimental study of aortic insufficienee 

 by operative rupture of the valve in animals 

 (dog, horse) was first made by Cohnheim 

 [AUg. Pathol, vol. i, p. 38, 1877) and by 

 Marey [Trav. de Laborat. p. 249, Paris, 

 1878). The problems raised, although in a 

 sense pathological, are answerable mainly by 

 physiological considerations ; for an excellent 

 account of these consult Marey, La Circu- 

 lation du Sang, pp. 677-80, figs. 325-6, 

 Paris, 1879. 



Obs. 38. Methylene-blue observation (P. 

 Ehrlich, 1886). This experiment shows that 

 the avidity of the tissues for oxygen is so 

 great that they are able to decompose the 

 methylene-blue molecule, with the formation 

 of a colourless reduction-product, which on 

 exposure to the air undergoes oxidation again, 

 and re-forms methylene-blue. ' If the tissues 

 are able to effect the reduction of a compara- 

 tively stable body like methylene-blue, it is 

 easy to understand their power of reducing 

 oxyhaemoglobin, which is so unstable that it 

 is decomposed by simple physical means such 

 as exposure to a vacuum.' — Starling. 



EXERCISE IX 



NERVl ACCELEEANTES ; GRAVITY AND ARTERIAL PRESSURE ; RECURRENT 

 LARYNGEAL AND THE VOCAL CORD. 



I. See that the decapitate preparation provided for you is being ventilated 

 suitably. 



II. Get ready the Hg manometer for arterial pressure, kymograph 

 (exerc. V), and electrical circuits for stimulating w^ith the hand-electrodes 

 (exerc. IV). 



III. Prepare the right carotid (exerc. Y) for blood-pressure observation, 

 but go no farther than passing the ligatures. Leave the dissection moistened 

 with Ringer-Locke and covered by replacing the skin, secured by a clip. 



