206 PRACTICE OF PHYSIC. 



haemorrhagy will be commonly at stated periods, as has been ob- 

 served frequently to happen. 



DCCXLIX. I have thus explained the nature of haemorr- 

 hagy in general, as depending upon some inequality in the 

 distribution of the blood, occasioning a congestion of it in partic- 

 ular parts of the sanguiferous system. It is indeed probable, 

 that in most persons, the several parts of the sanguiferous sys- 

 tem are in balance with one another ; and that the density, and 

 consequently the resistance in the several vessels, is in propor- 

 tion to the quantity of blood which each should receive ; from 

 whence it frequently happens, that no inequality in the distribu- 

 tion of the blood takes place in the course of a long life. If, 

 however, we consider that the sanguiferous system is constantly 

 in a plethoric state, that is, that the vessels are constantly dis- 

 tended beyond that size which they would be of, if free from any 

 distending force, we shall be satisfied that this state may be 

 readily changed. For as on the one hand the vessels are elastic, 

 so as to be under a constant tendency to contract upon the with- 

 drawing of any part of the distending force ; and, on the other 

 hand, are not so rigid, but that by an increase of the impetus of 

 the blood in them, they may be more than ordinarily distended ; 

 so we can easily understand how, in most persons, causes of an 

 increased contraction or distention may arise in one part or other 

 of the system, or that an unequal distribution may take place ; 

 and how, in an exquisitely distended or plethoric system, a small 

 inequality in the distribution of the blood may form those con- 

 gestions which give occasion to haemorrhagy. 



DCCL. In this manner I endeavour to explain how haemorr- 

 hagy may be occasioned at any period of life, or in any part of 

 the body : but haemorrhagies happen in certain parts more fre- 

 quently than in others, and at certain periods of life more read- 

 ily than at others ; and, therefore, in delivering the general 

 doctrine of haemorrhagy, it may be required that I should ex- 

 plain those circumstances which produce the specialties mention- 

 ed ; and I shall now attempt it. 



DCCLI. The human body, from being of a small bulk at 

 its first formation, grows afterwards to a considerable size. This 

 increase of bulk consists, in a great measure, in the increase 

 of the quantity of fluids, and a proportional enlargement of the 



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