322 EXPERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



in the experiments already mentioned, though, of course, to a 

 much more limited extent and with much less certainty. 

 3. The form of the curve, like those in Figs. 13 and 14, shows, 

 in the same way as those of the sphygmoscope, Figs. 1 3 and 14, 

 the rapidity with which the pressure falls during the diastole, 

 and from this curve and the amount of blood-pressure we can 

 judge of the size of the capillaries. 



Lecture V. — See Appendix, p. 643. 

 YI. — Eespiration. 



(Reprinted from the British Medical Journal, Feb. 13, 1875, p. 201.) 



Position of tlie Respiratory Centre ; chiefly situated in the Medulla Oblongata, 

 but extends also to tbe Spinal Cord. — Effect of Stryclmia upon it, — In- 

 fluence of Nerves upon it. — Influence of Yagus. — Yagus contains two sets of 

 Fibres, Accelerating or Inspiratory, and Retarding or Expiratory. — Cause 

 of Rapid Breathing in Pneumonia. — Influence of the Superior and In- 

 ferior Laryngeal Nerves. — Nasal and Cutaneous Nerves. — Local Action of 

 Yapours when inhaled. — Action of Ammonia. — Methods of Registering 

 Respiratory Movements. — Acceleration of Respiration by Drugs. — Is it due 

 to (1) Excitement of the Yoluntary Nerve-centres, (2) Increased Tempera- 

 ture, (3) Increased Yenosity of the Blood ? — Increased Yenosity may be due 

 to (A) Prevention of Blood from reaching the Air ; (B) Prevention of Air 

 from reaching the Blood. Blood may be prevented from reaching Air — 

 <(a) By Stoppage of the Heart : Action of Quinine. — {b) By Embolism of 

 the Pulmonary Yessels ; Action of Condurango. — (f) By Contraction of the 

 Pulmonary Capillaries; Action of Muscarine. — Observation of the Pulmo- 

 nary Capillaries in the Frog under the Microscope. — Effect of Heat and 

 Cold upon them. 



It used to be supposed that the respiratory centre was not only 

 situated in the medulla oblongata, but was confined to it. 

 Legallois found that ths cerebral hemispheres, cerebellum, and 

 even a part of the medulla itself, could be removed without 

 arresting respiration ; and thus showed that the respiratory 

 centre was either in the medulla or in the spinal cord. {Ex- 

 pSriences sur la Principe de la Vie. Paris, 1830, tome i) 

 Flourens noticed that injury to a point named by him nceiod 

 vital, at the lower end of the calamus scriptorius, instantly 

 arrested respiration, and thus caused death (Comptes Rendus, 

 vol. xxxiii, page 437) ; and all experimenters have found that 

 division of the cord just below the medulla also arrested 

 breathing. These experiments seem to show most conclusively 

 that the respiratory centre is situated in the medulla, and does 



