WHAT IS IT? ------------ This model demonstrates how the body's immune system defends itself against infectious bacteria or infectious disease. HOW TO USE IT ------------- To initialize the model, first click on the SETUP button. You will notice an array of red turtles scattered randomly about the screen in addition to a filled violet circle located in the center of the graphics window. The red turtles represent the "bacteria" and the filled violet circle represents the substance that manufactures the B-cells. Three sliders, called STEMRATE, BDEATH, and CLONEACT, located below the SETUP button, control the rate of released B-cells, the probability of B-cell death, and the probability of phagocyte reproduction, respectively. With regard to STEMRATE, the lower the number of the slider, the lower the number of B-cells the filled circle releases ( and vice-versa). With regard to BDEATH, the lower the number of the slider, the quicker the B-cells die (and vice-versa). With regard to CLONEACT, the lower the number of the slider, the more the phagocytes reproduce into other phagocytes. Prior to pressing SETUP, configure these three sliders to whatever numbers you may wish (DEFAULT INITIAL SETTINGS: STEMRATE = 5, BDEATH = 5, CLONEACT = 10). After configuring these three sliders, activate the model by clicking on the GO button. THINGS TO NOTICE ---------------- Under the default initial slider configuration of STEMRATE = 5, BDEATH = 5 and CLONEACT = 10, notice that at first there are only a few B-cells that the filled violet circle releases. As time advances, these B-cells die and a few more are released that replace them. So at every given point during the simulation, there is a steadily increasing number of Bcells. Notice also that the number of phagocytes is extremely small at the beginning but, as the simulation continues, they slowly increase and then, all of a sudden, explode, and seem to be everywhere. This phenomenon is indicative of the B-cells sensing the bacteria and then cloning themselves into self-reproducing phagocytes. THINGS TO TRY -------------- What happens when you set the CLONEACT on its maximum level? How does this affect the rate at which the phagocytes reproduce or clone themselves? Play around with the sliders. What happens when you set each slider to its maximum and minimum values? EXTENDING THE MODEL -------------------- This model may not only be helpful in demonstrating the phenomenon of our immunity system but it might also be helpful in illuminating some of the mechanisms of cancer growth. Try extending this model in such a way that demonstrates how the phagocytes can reproduce at a large, uncontrollable rate indicative of cancer formation. STARLOGOT FEATURES ------------------- This model, in particular, makes good use of the *output* function in a simple and understandable way. The output function takes an argument and returns it to the caller. The model used this function in order to represent the changing number of bacteria, B-cells, and phagocytes remaining on the graphics window at every point in time during the model's simulation.