I used to crack open my old copy of the  Merck Manual  to see whether I had symptoms of the disease listed on any random page. Usually I did, but that was just me.

Now, I can do the same thing on my smartphone.

The Merck Manual Home Edition is a $9.99 app version of the venerable medical tome from Agile Partners Technologies L.L.C. Once loaded onto your mobile device, the nearly 20MB app doesn't require a data connection to function.

Of special note is the button for "Emergencies & Injuries" on the home screen that switches on a list of unfortunate events that might make the app incredibly handy - allergic reactions, poisoning, human bites, burns, and nosebleeds. Just remember to call 911 first.

True,  Merck Manual content is free on the Web at www.merckmanuals.com, but the app is well-organized, portable, and compelling. It'll hold a history of the items you've browsed and a list of favorite pages.

As a free app alternative, the Medical Encyclopedia, from the University of Maryland Medical Center, is a comprehensive reference that, among many things, links to the medical center's extensive collections of videos on YouTube.

Got symptoms? Once you know which disease you have, look it up on iHomeMD and you'll get a list of the likely prescription and over-the-counter medications that might help fix where you're hurt. The $1.99 app, by Feng Laboratory L.L.C. for Apple and Android devices, has information on 400 diseases and 3,000 drugs, which isn't comprehensive, but you're probably covered.

Now, picture sitting in the doctor's office and being told you ought to be taking a statin for your high cholesterol. While the doctor pauses to check her e-mail or the stock market, you could whip out your phone and run down details of the medication by using the Micromedex Drug Information app, a freebie from Thomson Reuters (Healthcare) Inc.

This app is aimed at health professionals, but for consumers it provides exhaustive details about drugs, the medicines they may interact with, and warnings on their usage. It also lists both a drug's Food and Drug Administration-approved uses and those uses considered "off-label," for which the drug may be commonly prescribed but not FDA-approved.

WebMD's free app delivers general health information. It combines much of what's available from the previous two apps with a huge supply of articles and features for exploring health issues, drugs, and other treatments, first aid, and resources such as groups that do research or advocacy for specific diseases and conditions.

Tap on a body part on the "Symptom Checker" diagram and you can drill down to possible causes for your discomfort and articles about it.

Contact staff writer Reid Kanaley at 215-854-5114, rkanaley@phillynews.com, or @reidkan on Twitter.