166 Biographical Account of [March, 



collection of his experiments and conclusions under the title of 

 " Haemastatics, or Statics of the Blood." 



He exhibited in fact a measure, and an exact measure, of the 

 force with which the heart forces the blood through the body of 

 the animal. He fixed transparent tubes to various arteries of 

 living animals, and thus observed, by the height to which the 

 blood rose in them, the force with which it was driven by the 

 heart in the different circumstances examined by Dr. Hales. 

 Sometimes the animal was possessed of its full strength ; some- 

 times its strength was diminished by the abstraction of a deter- 

 minate quantity of blood, or by a variety of other ways which it 

 would be too tedious to describe here. The effect of these 

 changes on the height to which the blood rose in the tube, on 

 the frequency of the pulse, and upon the whole state of the 

 animal, are carefully observed, and from them a vast number of 

 useful and curious consequences are deduced. He shows, for 

 example, that profound inspirations and frequent contractions of 

 the lungs increase the velocity of the blood, and .that yawning 

 has the necessary consequence of accelerating the flow of the 

 blood through the lungs. He shows likev'ise that too great a 

 loss of blood, instead of diminishing, actually increases the rapi- 

 dity of the flow of blood through the arteries. He extracted the 

 whole blood from animals, and substituted in place of it water 

 heated to the same temperature ; but the life of the animal was 

 not supported. Thus he showed that the blood does not act 

 merely as a liquid ; but as a substance of a peculiar kind. 



His observations on anatomical injections ai'e of great import- 

 ance, and give quite a new view of that subject. The object of 

 anatomists, in injecting the veins and arteries of animals, is to fill 

 them with a liquid, which afterwards becoming solid, may 

 exhibit these vessels of the same size as they possess in the 

 livino; animal. But as (bese vessels are extensible, it is obvious 

 that if the matter of the injection be pushed with greater or less 

 violence than the blood was pushed on in the living animal, the 

 vessel will in consequence be more or less distended than in the 

 living animal, and consequently the capacity of these vessels will 

 no longer be the same as in the living animal. To remedy this 

 inconvenience, Dr. Hales employed, to push on an injection, a 

 column of liquor, which he renders equal in force to that exer- 

 cised by the heart during the life of the animal. Of the amount 

 of this force he had satisfied himself by his previous experiments. 

 This method of proceeding enabled him to judge with much 

 greater accuracy (han former anatomists of the capacity of the 

 diflerent vessels through which the blood flows. He measured 

 the diameters of each, and endeavoured to determine by calcu- 

 lation the velocity with which the blood moves in the diflerent 

 vessels. He determined the facility with which different liquids 

 could pass through the blood vessels, by ascertaining the height 



