What does "assimilation" mean?

Assimilation: (Physiol.) The conversion of nutriment into the fluid or solid substance of the body, by the processes of digestion and absorption, whether in plants or animals. Not conversing the body, not repairing it by assimilation, but preserving it by ventilation. Sir T. Browne. Note: The term assimilation has been limited by some to the final process by which the nutritive matter of the blood is converted into the substance of the tissues and organs.