A healthy immune system has two components. Discrimination distinguishes your pet’s own normal organisms from dangerous invaders. Recognition detects foreign organisms through the lymph nodes. Natural reactions begin, warding off the threat. This takes time, however, and first-time invaders sometimes produce illness. Severity depends on exposure and seriousness of the foreign agent. If first-time invaders are destroyed, the body builds immunity and later invasions of the same agent are blocked more rapidly with little or no illness.
