TO DE. HAYGARTH. 289 



likely to deceive us as a pair of spectacles, which, as is allowed 

 by all who use them, do not disfigure objects, but only repre- 

 sent them larger. 



From further experiments, I am convinced that the use of 

 the thymus and lymphatic glands is to make the solid middle 

 pieces ; and I can prove it in as satisfactory a manner as you 

 can do the use of any viscus in the human body ; that is, by 

 opening these glands, and examining the fluid contained in 

 their cells, which I find to be full of these little solids. I 

 moreover find that the lymphatic vessels take them up from 

 those glands, and convey them into the blood-vessels, which 

 carry them to the spleen, in whose cells they have the vesicles 

 laid over them ; so that the thymus and lymphatic glands make 

 the central particles, and the spleen makes the vesicles that 

 surround them. That this is the use of the spleen, appears 

 from examining the lymph which is returned from it by its 

 lymphatic vessels, which are its excretory ducts ; for that lymph, 

 contrary to what is observed in other parts of the body, is 

 extremely red. 



But, besides having these glands set apart for making the 

 red vesicles of the blood, I find that they are also made in the 

 lymphatic vessels in different parts of the body, whose coats 

 have blood-vessels properly constructed for this secretion. So 

 that the thymus. and lymphatic glands are no more than ap- 

 pendages of the lymphatic system, for making the middle 

 particles ; and the spleen an appendage to the lymphatic vessels, 

 for making the vesicles which contain these middle particles. 



I conjecture that it is the coagulable lymph which is con- 

 verted into this red part of the blood, from a curious fact that 

 has been long known ; namely, that the blood in the splenic 

 vein does not coagulate, when exposed to the air, as the blood 

 of other veins does (CLI) ; so that it seems to be robbed of its 

 coagulable lymph in passing through the spleen. 



It is very remarkable that the spleen can be cut out of an 



(CLI.) Mr. Hewson perhaps only had in mind the fact, mentioned 

 in Note cxxxn, page 269, that the blood of the splenic vein generally 

 coagulates less perfectly than other venous blood ; and not that the 

 blood of the splenic vein remains entirely fluid, until it dries, when ex- 

 posed to the air, as Mr. Falconar's statement, at page 283, sect. 99, 

 would imply. 



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