To be perfectly honest, most wildlife "rehabilitation" books & guides are not designed to actually save lives, they're designed to end them. It's a fact, albeit a sad one.
BEFORE YOU START: Do not feed a cold animal- if you just found an orphaned baby critter, be sure the animal is warm BEFORE you feed it or it will be unable to digest the food and will die. Place a towel over a heating pad and gently & slowly warm the critter before feeding.
First and foremost, if you have a pet nursing bottle, throw it away. It will NOT work for your squirrel- what it WILL do is cause them to aspirate formula and give them pneumonia (which is essentially SLOW drowning).
If you aren't sure whether you can control the flow of the syringe or not, I recommend practicing with warm water so you don't accidentally drown the baby critter you're attempting to help.
a 1 ml Syringe
1 c. Whole Cow's Milk (yup, straight from the gallon in the fridge, and don't use that nasty low fat or 1% stuff!!)
4 drops of Vitamin E (from a 200 IU capsule) poke the capsule, squeeze gently
Scald the milk- if you're not familiar with this term it means to heat the milk just to boiling point but do NOT boil it!. Remove from heat, add the vitamin E, mix with the handle of a wooden spoon.
You can also scald milk in the microwave. Measure 1/3 c. of milk into a mason jar (uncovered) heat on high for 25 seconds, stir with wooden spoon, heat additional 25-30 seconds
Feed warm formula every 4 hours, round the clock. Do not skip nighttime feedings as your baby critter will die.
Do Not Neglect to Scald the Milk or your baby critter WILL die. Do not feed your baby critter crap like "Commercial Puppy Formula or Esibilac, which IS toxic to it and they WILL die.
Please note, depending on how young the baby squirrel, rabbit, etc is, you may need to stimulate it to go to the bathroom following a feeding. You can do so by wetting a paper towel with warm water, (ring it out thoroughly) and washing the critters genitals very gently, stimulating it in the same way it's mother would. If you find this abhorrent, then you should immediately call a Wildlife Rehab specialist in your area as the little one you found is likely to die otherwise.
Scalded Milk WITHOUT egg yolk (unborn chicken) is recommended for ALL vegetarian animals, babies or adults (when needed),including deer, rabbits, mice, rats (wild and domestic), hamsters, gerbils, guinea pigs, as well as all types of tree squirrels or ground squirrels including flying squirrels, prairie dogs, chipmunks, groundhogs, marmots, beaver, and nutria.
See Also: Complete Nutrition Nut Balls for Squirrels
For a Full and Complete Detailed Rehabilitation Guide for Raising Orphaned or Injured Baby Squirrels (& rabbits) please see This Amazing Resource by Clarissa Summers. We have used her guide to successfully raise 23 squirrels (that's a 100% Success Rate folks) and 2 baby rabbits.
Here are photos of Very Happy Healthy Squirrels who have been raised on the Scalded Milk/Nutball Diet.