Well, it's not quite as ubiquitous as a communicator, phaser, or tricorder, but it almost
Dr. McCoy's hypo spray was used in a lot of episodes--not only in Sickbay scenes, of course, but on landing parties, too. (It was one of the pieces of equipment he would carry in his various Medical Pouches.)
The first time we see a hypo spray device is in "Where No Man Has Gone Before:"
There are actually two styles of hypo sprayers. The first style (used throughout the first season) is a "sleeve" style injector. The length of the device remains rigid and the device doesn't
telescope into itself. Instead, there is a hand-grip sleeve that slides up and down the main shaft of the device. Aside from "Where No Man Has Gone Before," the first regular production episode to use this "sleeve" type of hypo is "The Enemy Within." Mister Spock uses it to inject the "evil" space dog to sedate it in preparation for reintegration with the dog's other half via the transporter:
The second style of hypo--seen in the second and third seasons--actually telescopes. Ostensibly, it looks nearly identical to the "sleeve" style hypo. It consists of a somewhat pointy "business end," a plunger and a detachable/replaceable vial of "medication" fluid at the rear. Although this is a shot of the first type of hypo, here's a scene from "City On the Edge of Forever" where Mister Spock has removed the vial to find that it is now empty--the entire volume of Cordrazine having just been accidentally injected into Doctor McCoy:
Different color fluids were used in different episodes to indicate different medications. We've seen mostly red and orange fluids (probably since red makes them seem dangerous and exciting--but we've seen blues and greens, too).
Selecting the best color for any given shot is probably a joint effort between the property master, the director, the director of photography, and the lighting team--especially in an era where Star Trek Phase II
shoots with High Definition cameras. Series continuity plays a role too. I mean, otherwise you end up having the annoying problem (well, annoying to me at least) of seeing Cordrazine be red colored in "City on the Edge of Forever"...
...but then having it be Sunkist/Orange Crush-colored when Nurse Chapel gives Cordrazine to Ensign Rizzo in "Obsession:"
In addition to the early "sleeve"-style hypo, they had at least three telescoping-style hypos produced. Here's a shot of three of the hypos together from "Return to Tomorrow." It's a little hard to see in this screen grab, but the hypo in Nurse Chapel's hand that contains Sargon's ineffective "metabolic reduction medication" has fluid in it that is indeed a slightly different color (more orange) from Henoch's and Thalassa's more efficacious red fluid.
At any rate, here are some shots of my reproduction Original Series-era telescoping-style hypo spray:
You can see that I have a number of accompanying medication vials of varying colors--whatever meets our cinematic and script needs. It's easy to swap out a red vial, for example:
...and replace it with a yellow vial.
There are important medical matters going on in the Phase II
episode "Blood and Fire." So our hypo sprays figure prominently in that episode.
Obligatory slideshow is at:http://www.flickr.com/photos/10901121@N06/sets/72157603748995814/show/