Again, if more than 2% of carbon is present, it passes readily into the state of pure graphitic carbon, which, in itself soft and weak, weakens and embrittles the metal as any foreign body would, by breaking up its continuity.
If this carbon is all present as graphite, so that in cooling the graphite-austenite diagram has been followed strictly (§ 26), the constitution is extremely simple; clearly the mass consists first of a metallic matrix, the carbonless iron itself with whatever silicon, manganese, phosphorus and sulphur happen to be present, in short an impure ferrite, encased in which as a wholly distinct foreign body is the graphite.
Thus the poison of various insects induces in plants the cellular new formation known as a gall-nut; a foreign body implanted in a limb may become encysted in a capsule of fibrous tissue; septic matter introduced into the abdomen will cause proliferation of the lining endo(epi)thelium; and placing an animal (salamander, Galeotti) in an ambient medium at a higher temperature than that to which it is accustomed naturally, increases the rapidity of celldivision of its epithelium with augmentation of the number of karyokinetic figures.
This was similar with respect to quinsy drainage and foreign body removal from the ear, nose and throat.
Instead of ignoring pet dander or pollen, it mistakenly identifies it as a foreign body such as a virus, and trigger's the body's immune system response to combat it.
