THE BLOOD. 67 



Simson's observation (xxxii), but then it will probably be only 

 in small quantity. 



The same learned gentleman, on being informed of the re- 

 sult of this experiment, ingeniously suggested that the quantity 

 of blood which I had taken away might perhaps be too little to 

 make the experiment decisive ; for, as only one ounce of blood 

 had been taken from each arm, all that blood might be supposed 

 to have been contained in the veins themselves ; and as it was 

 more probable that the disposition to size took place in the 

 arteries, a larger quantity should be taken away, in order to 

 judge whether the blood in the arteries had not been changed 

 by the veins of the arm being so long compressed.. The ex- 

 periment was, therefore, repeated upon the same person, on the 

 7th of March, Mr. Field and Mr. Hendy assisting me as 

 before, and we observed as follows : 



EXPERIMENT XXXIII. 



The blood from the arm first opened was in quantity about 

 ten drachms, had no size, but was late in being completely co- 

 agulated. The pellicle first appeared on its surface six minutes 

 after opening the vein, and at the end of fifteen minutes a con- 

 siderable quantity of the blood was still fluid ; but in thirty-four 

 minutes it was completely coagulated. The serum did not begin 

 to ooze out till at the end of fifty minutes. 



After the other arm had been tied up an hour, the vein was 

 opened, and about ten drachms of blood were received into the 

 first cup, as much more into a second, and about an ounce 

 and a half upon a pewter plate, and about two ounces and a 

 half into a third cup (in all six ounces and a half) ; and it was 

 observed that the blood in the third cup and that in the second 

 coagulated in about twenty minutes, and the serum began to 



(xxxu.) Thomas Simson a thought that the buffy coat is formed of 

 crude chyle not yet converted into blood ; and that the buff appears 

 after putting a ligature for three or four hours on the thigh or arm, 

 because the assimilation of the chyle with the blood is thus prevented. 

 Mr. Hey b found that neither the tightness of. the ligature, nor its longer 

 continuance than usual on the arm, caused the blood to become buffy. 



a DeRe Medica, 8vo. Edin. 1726, Diss. b Obs. on the Blood, 8vo, Lond. 1779, 

 iii, $38, p. 112. p. 65. 



