Failed to understand the meaning of "only" here

In "which in turn damage only certain organs", it seems "only" can be removed without affecting the meaning.
What do you think?

Context:
No one wishes to dispense with the blessings of modern medicine, which took away the dread of many diseases. The flipside of the coin: To ensure that effective and safe medications are available, experiments on animals in research laboratories are indispensable. Throughout the world, researchers are working on alternatives to animal experiments. Yet it is difficult to find a substitute. Because in order to understand the effect of a substance, it is not enough to test the substance on isolated tissue samples or cells. "Most medications work systemically -- that is to say, on the organism as a whole. In doing so, toxic substances frequently emerge through metabolic processes, which in turn damage only certain organs," explains Dr. Frank Sonntag of the Fraunhofer Institute for Material and Beam Technology IWS.

MOre:
http://www.sciencedaily.com/releases/2015/02/150202080638.htm