162 LYMPHATIC SYSTEM. 



the more viscid or coagulable; instances of which occur in 

 those inflammatory crusts that are found, in some diseases, to 

 cover the different parts of the body. Thus the outside of the 

 heart and the inside of the pericardium are sometimes covered 

 with a crust as tough as the size in pleuritic blood, and the 

 surface underneath has marks of inflammation, but is not 

 ulcerated (LXXII). Probably, therefore, it is the inflammation 

 which produces that change, or which makes the exhalant 

 arteries secrete a lymph with such an increased disposition to 

 coagulate. Add to this, that the change which inflammation 

 thus seems to produce is just the opposite to that produced by 

 the dropsy, for in the dropsy the fluid is secreted with an extra- 

 ordinary quantity of water and too little coagulable matter ; 

 but in inflammations the fluid is secreted with a greater pro- 

 portion of coagulable matter, and with less water ; and in some 

 instances it seems to be a pure coagulable lymph, either un- 

 changed by the exhalants, and then coagulating gradually on 

 being at rest, as the coagulable lymph is found to do in the 

 veins that are tied; 1 or else the exhalant vessels have the 

 power of changing its properties, so as to make it coagulate 

 in an instant after being secreted. And this supposition of 

 the exhalants having a power of changing the properties of the 

 lymph is rendered probable from the following consideration, 

 viz. that it is sometimes found coagulated in the inner surface 

 of the heart, forming a crust, similar to what we so often see 

 on the outside. Now as there is a constant current of blood 

 through the heart, unless the lymph forming that crust had 

 coagulated instantly on being secreted, it must have been 

 washed off by the blood. One of the clearest instances of 

 this was observed by Sir John Pringle, who has given me 



1 See Exp. Inquiries, part i, p. 22. 



(LXXII.) Dr. William Hunter, as early as the year 1/57, observed 

 that pus may be formed without any breach in the solids ; and John 

 Morgan/ of Pennsylvania, soon afterwards described pus as a secre- 

 tion. The coagulated lymph on inflamed serous membranes, here and 

 at page 164, so accurately characterized by Hewson, Dr. Hunter called 

 " a glutinous concretion, or slough." See the Introduction. 



a De Puopoiesi, sive Tentamen Medicum Inaugurate de Puris Confectione, p. 5, 8vo, 

 Edin. 1763. 



