THE BLOOD. 65 



and where therefore, in the ordinary manner of bleeding, there 

 would have appeared but very little size, such blood, if more 

 exposed to the air so as to be sooner cooled, may thereby have 

 the small degree of attenuation counteracted, or removed, and 

 the red particles may be prevented from subsiding. So that 

 although in this experiment, where the size was thick, it ap- 

 peared equally in the saucer as in the cup, and even appeared 

 on the blood upon the plate; yet, if we repeat these experi- 

 ments on a variety of subjects, it is probable that we may 

 sometimes find the saucer without a size, whilst the cup has 

 one ; for when the lymph is but little attenuated a slight cause 

 may thicken it again ; and its being a little more cooled in the 

 saucer and on the plate may in some cases be sufficient to 

 prevent the size from appearing. 



It has likewise been suggested, that possibly there might be 

 some difference in the orifice from which the blood flowed, to 

 which its different appearances in the several cups might be 

 owing. But there does not seem to be any foundation for this 

 objection, and it may, I think, be removed by a careful exami- 

 nation only of some of these experiments, particularly the 27th ; 

 for there the blood ran into a full stream both into the second 

 cup and into the third, the orifice being apparently unaltered, 

 and yet there was a great difference in the appearance of the 

 blood : for that in the third cup had a thick size, but that in 

 the second had none. So that there does not seem to be any cir- 

 cumstance attending these experiments that can explain the 

 changes produced upon the blood in the time of bleeding, ex- 

 cepting that to which I have attributed it, viz. a change in the 

 strength of the blood-vessels, or in their mode of action ; and 

 every observation I have yet made confirms me in that opinion. 



A very eminent physician, 1 after reading the first edition of 

 these sheets, informed me, that from a suggestion which he 

 met with in Professor Simson's Dissertations, viz, "That a 

 ligature on the arm wo.uld produce a size," 3 he had been for 

 many years cautious how he took any indications from this ap- 

 pearance of the blood, and desired I would endeavour to deter- 



1 Dr. Fothergill. 



2 Dr. Simson's observation is, that if a tight ligature be made on the limb, and the 

 vein opened three hours after, a size will be produced. Vide ' De Re Medica,' 

 Dissert, iii, 38, p. 112. 



