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if the fubje&s be really of the fame kind; if no 
difference can be fhewn between them, in any refpeCt 
material to the inquiry, in which we are engaged ; 
in this cafe our inference from analogy becomes the 
very next thing to a phyfical certainty : and this I 
apprehend to be true in relation to the problem be- 
fore us, concerning the origin of the lymphatic vef- 
fels. Tho’ in general we cannot, by experiments, 
arrive at the extremities of thofe tubes, nor fatisfy 
ourfelves, by infpeCtion, in what manner they receive 
their fluid ; yet in a very confiderable number of 
them we can do both. There is a certain part of 
the human body very abundantly provided with lym- 
phatics ; in which part we can actually force in- 
jections thro’ thofe veflels into a cavity, where their 
extremities open : and from this cavity, on the other 
hand, we can at pleafure introduce a coloured liquor 
into their extremities, and trace it from fmaller into 
wider canals ; from capillary tubes, without valves, 
into large lymphatic trunks copioufly furnifhed with 
them. We know likewife, that into this cavity are 
continually exhaling an infinite number of watery 
and mucous veflels, both arterial tubes and excretory 
duCts : that thefe keep it moift with a perpetual va- 
pour, which the extremities of thofe lymphatics are, 
in the mean time, perpetually imbibing. Does it 
not feem flrange, while thefe particulars are known 
and acknowleged by all the world, that the great 
authors of anatomy and phyfiology fhould never have 
reafoned from them ; but fhould run into complex 
and obfcure fuppofitions, in order to explain a pro- 
cefs, which they may at any time examine with their 
own eyes ? But perhaps this inadvertency may be 
accounted 
