$\frac{d \mathrm{CS2}}{d \mathrm{time}}=\mathrm{lambda\_ER\_S2}\mathrm{JIPR}-\mathrm{lambda\_S1\_S2}\mathrm{JS1S2}+\mathrm{lambda\_MT\_S2}\mathrm{JMCU}\mathrm{lambda\_MT\_S2}=\frac{\mathrm{gamma\_MT}}{\mathrm{gamma\_S2}}\mathrm{lambda\_ER\_S2}=\frac{\mathrm{gamma\_ER}}{\mathrm{gamma\_S2}}\mathrm{lambda\_S1\_S2}=\frac{\mathrm{gamma\_S1}}{\mathrm{gamma\_S2}}$