The vials are easily interchangeable, which is a particularly useful feature for the Emergency Medical Hologram aboard Voyager, as he often works alone. The normal crew complement of an Intrepid-class starship such as Voyager includes a permanent nurse. This post has not been replaced although Kes acted as trainee nurse and assistant until she left Voyager in 2374, and Lt. Tom Paris, who had some medical knowledge, was assigned in 2371 to assist the Doctor.