INTRODUCTION. 



XXXIX 



him the better to investigate the properties of the lymph, apart 

 from the red corpuscles, he kept it fluid by neutral salts, and 

 proved that it would yet coagulate after the addition of water. 

 He showed from precise observations how much longer coagu- 

 lation is in taking place when the blood is stagnated, either 

 artificially or from natural causes, in its own vessels, than when 

 it is removed from them. His experiments on the comparative 

 rate in the sinking of the red corpuscles in what has since been 

 called the liquor sanguinis and in the serum were highly novel, 

 ingenious, and correct. 1 He described accurately the part per- 

 formed by the coagulable lymph in diseases ; how the fluid of 

 dropsies differs from that lymph and from the serum; and 

 carefully examined the properties of the fluid of the lymphatic 

 vessels and of the serous sacs. The theoretical conclusions to 

 which he was led by those inquiries, on the secretion of lymph 

 into serous sacs and on the pathology of the lymphatic system, 

 contain the sum of nearly all that is at present known on those 

 subjects. 



In considering the labours of Hewson in connexion with 

 the facts observed and the errors held by his predecessors and 

 contemporaries, it must be recollected that the speculations 

 connected with Leeuwenhoek's microscopical researches for 

 many years supplanted accurate experimental inquiries into the 

 properties of the blood ; so that the fibrin was either forgotten 

 or confounded with the serum, and a fanciful importance was 

 given to the red corpuscles. When the errors consequent on 

 this state of things began to wane, the blood sunk into neglect. 

 Accordingly, the just observations of Malpighi, Lower, and 

 Borelli, were lost for the greater part of a century, while the 

 coagulation of the blood was ascribed to a mere cohesion or 

 running together of the red corpuscles, and the formation of 

 fibrinous clots to a change in the serum. These opinions were 

 held in Britain by the best writers to the year 1760, and on 

 the Continent by the most distinguished physiologists, as Haller 

 and Marherr, up to or even beyond 1771, the date of the first 

 edition of Hewson's ' Inquiry into the Properties of the Blood/ 

 But there were exceptions. The knowledge of Petit, Quesnay, 

 Senac, and Gaubius, was unquestionably in advance of that 

 current in their day; yet they added but little to the facts of 

 1 See Note xxm, p. 40. 



