Take, for instance, inflammation. When germs are beneath the skin, one finds redness, swelling, heat, pain, as the symptoms of inflammation. What does that mean? It is all like the defences which were set up round Paris when the Germans were coming there, or that are set up anywhere when one is getting ready to repel attack. The inflamed finger gets red because a great deal of blood is going there. The blood cells, especially the white cells of the blood, are coming there to defend. The finger gets red for the same reason that the railroads get congested in time of battle, namely, because so many soldiers are being carried there for defence. The finger gets swollen because so many cells and fluids are coming to attack the enemy; it is their crowding outside the blood vessels that makes the swelling. There is heat in the finger because there is more blood in the part and therefore the part is hotter. There is pain because with the extra accumulation of defenders there is a squeezing of the little nerve terminations there. When a lot of soldiers are suddenly quartered, billeted in a town, it is a painful process. There is pain in having defence come to your city. There is pain in having defence come to your finger. All of these symptoms, which we are apt to hate and to think of as misfortunes, we should realize are the thing which saves us from very serious illness. Suppose these things did not happen. Following out the metaphor, if it were not for these defences the enemy would penetrate into the whole body and we should have blood poisoning. It is because this local heat, redness, swelling, pain, appears at the point where bacteria are attacking us, that they do not penetrate the whole body with a _septicemia_, which is one of the most dangerous of all diseases. So while suffering what we must suffer, we ought to be glad of all that nature is doing, because if she neglected it the consequences would be very serious to us.