AMMAL MECHANICS. 



139 



No. 



Maximum height 

 before loss of blood. 



Minimum Height. 



Total Blood lost. 



i. Mare, 



8.25 feet. 



2.33 feet. 



924 cub. in. 



2. Gelding,. 



9.66 „ 



2.83 „ 



895 » 



3. Mare, 



9-5° m 



2.42 „ 



833 » 



Mean, 



9.14 feet. 



2.53 feet. 



884 cub. in. 



It appears from the foregoing table that the minimum con- 

 traction of the horse's heart, corresponding to the resistance 

 offered by a circulation almost drained of its blood, amounts 

 to the pressure of a column of blood 2.53 feet in height. Dr. 

 Hales has also recorded the important fact, that the crural or 

 carotid artery of the horse, when first cut and allowed to spout 

 freely, does not throw the blood much higher than 2 feet. 

 It would appear from this observation that the cutting and 

 free exposure of a cut artery to the air relieves the heart at 

 once of the resistance offered by the capillary circulation, for 

 otherwise it is difficult to understand why the blood should 

 not spout upwards through 9 feet instead of somewhat over 

 2 feet. 



Experiments on the pressure of the blood inside the human 

 heart, similar to those of Dr. Hales on animals, have not yet 

 been made ; but it is estimated at 7.5 feet by Dr. Hales from 

 considerations founded on the comparative bulks of the soft 

 parts of man and of the horse supplied/by the arterial circula- 

 tion. 



The following observation and calculation of the velocity 

 of blood spouting from a large artery in man, lead, as I be- 

 lieve, to a more correct estimate, although indirect, of the 

 pressure of blood inside the left ventricle. 



On the 1 8th of March, 1863, a large fibro-cellular tumour 

 was removed by Mr. M. H. Colles, in the operating theatre of 

 the Meath Hospital, from the left groin of a middle-aged, 



