ARTERIAL PRESSURE. 



263 



The experiment with the long tube gives us the best idea 

 of the arterial pressure, which will be found to vary from five 

 and a half to six feet of blood, 

 or a few inches more of water. 

 The oscillations produced by 

 the con tractions of the heart are 

 not very marked, on account of 

 the immense friction in so long 

 a tube ; but this is favorable to 

 the study of the constant press- 

 ure in the arteries. It has been 

 found that the estimates above 

 given do not vary very much 

 in animals of different sizes. 

 Bernard found the pressure in 

 the carotid of a horse little 

 more than in the dog or rab- 

 bit. In the larger animals it 

 is the force of the heart which 

 is increased, and not to any 

 considerable extent the con- 

 stant pressure in the vessels. 1 



The experiments of Hales 

 were made with a view of cal- 



thp fovopof thp hpart Section of the cardiometer of Magendie, as 

 Gart 5 modified by Bernard. A strong glass bottle 

 is perforated at each side, and fitted with an 

 iron tube, with an opening, T, by which the 

 mercury enters. One end of the iron tube 

 is closed, and the other is bent upwards and 

 connected with the graduated glass tube T', 

 which has a caliber of from ^ to of an inch. 

 The bottle is filled with mercnry until it 

 rises to n' in the tube which is marked O. 

 The cork is perforated by the tube t, which 

 is connected by a rubber tube with the point 

 C, which is introduced into the vessel. 

 (BEKNARD, Liquid 'es de VOrganisme, Paris, 



that we have any reliable data. ie J " p ' 16T 



on this latter point. 2 Poiseuille's instrument for measuring 



the force of the blood is a simple graduated U tube, half 



and were not directed particu- 

 larly to the conditions and va- 

 riations of the arterial pressure. 

 It is only since the experiments 

 performed by Poiseuille with 

 in 1828, 



1 BERNARD, lAquides de VOrganiftmc, Paris, 1859, tome i., p. 172. 



9 POISEUILLE, Recherches sur la Force du Cceur Aortique, Paris, 1828. 



