374 THE CIRCULATION OF THE BLOOD. CHAP. XXVIII.] 



which permits them to receive a greater quantity of blood from 

 the heart, and to a minus state of the capillary force, the other 

 to a, plus condition of that force, in virtue of which the tissue at- 

 tracts a greater quantity of blood. To this latter form of con- 

 gestion, pathologists give the name of inflammation. Its pheno- 

 mena, as observed under the microscope, are such as a vis a tergo 

 alone could not develop. For not only are there dilatations of the 

 vessels of the inflamed part, and a great afflux of blood towards a 

 certain point or points in it, but the blood corpuscles seem to rush 

 thither, as if forcibly attracted towards each other, and also to some 

 common focus. And the rapid and copious process of exudation, 

 and the formation of pus-cells, which are so apt to follow an attack 

 of inflammation, afford further strong indication of augmented vital 

 force in the inflamed part.* 



So also in growing tissues, and in organs which enlarge at 

 particular times, or under certain circumstances, the increased 

 flow of blood to the part is a phenomenon in close analogy 

 with the increased flow of sap to a bud ; and is due not to a vis 

 a tergo, or to a relaxed state of blood-vessels, but to a demand 

 from the tissue for more blood, an attractive force, by which the 

 direction is regulated, and the quantity also. The annual re- 

 newal of the antlers of the stag, the enlargement of the testes of 

 birds at particular seasons, that of the breasts of women during 

 pregnancy and after parturition, all these cases afford instances in 

 which a demand for blood is created at some point of the periphery, 

 and a greater flow is established to the organs there placed than 

 previously took place to them. 



We can afford no satisfactory explanation of the localization of 

 certain changes in the capillary circulation, unless on the hypothesis 

 that the constituent elements of the affected parts are primarily 

 diseased, and that their demand for blood is, in consequence, 

 increased or diminished, and the flow of blood regulated accord- 

 ingly. Thus the development of gout in a joint takes place often 

 with such rapidity that it appears to the patient to be sudden ; the 

 train of phenomena being in such cases, first, a change in the tissues, 

 so gradual as to be unperceived, then, an increased flow of blood to 

 such an extent as to cause the heat, the throbbing, and pain which 

 characterize such affections. Again, certain poisons, which seem as 

 it were to spend their force, in great part at least, on the skin, do 

 not cause a change in the whole capillary circulation so much as 



* The theory of inflammation is extremely well discussed in Mr. J. Simon's 

 Lectures on Pathology, Lect. IV. See also Mr. Paget's Lectures on inflammation. 



