Complex sentence: From that position he pushed the introduction of modern medical instruments like the thermometer and the hypodermic syringe, which was used to administer morphine, atropine and cocaine in the treatment of patients.
Split into simpler sentences: From that position he pushed the introduction of modern medical instruments like the thermometer and the hypodermic syringe. The latter was used to inject morphine, atropine and cocaine in the treatment of patients.