Which of the following treatments irritated patients’ eyes and lungs during operations?

The correct answer is ether. Ether was one of the first anesthetics used in surgical procedures, and it was administered by inhalation. While it was effective in rendering patients unconscious during operations, one of its significant drawbacks was that it caused irritation to the eyes and lungs. Patients often experienced coughing or irritation due to ether's pungent and volatile nature. Ether also had a tendency to be highly flammable, adding further risks during surgery.

Understanding this characteristic of ether is crucial as it highlights the challenges of anesthesia prior to advancements in safer anesthetic agents. In contrast, chloroform, ethanol, and nitrous oxide had different effects and usages during this period in anesthesia. While chloroform is known for its effectiveness, it did not primarily irritate the eyes and lungs to the same extent as ether. Ethanol, used in a different medical context, was not typically used as an anesthetic in this manner, and nitrous oxide, although it can cause respiratory effects and sedation, does not primarily induce irritation of the lungs and eyes like ether does. This distinction is key in understanding the development and eventual changes in anesthetic practices in the medical field.