@JeannieCO its for if they get severely over heated, breathing becomes very rapid laboured and noisey almost roaring, the tongue at this stage will most likely be blue.
secretions become thick and hinder breathing. squirt the lemon in the back of the throat it boosts the salivary glands and they are able to swallow if its not too bad or they will vomit clearing the throat
however the lemon is only a part of it If they are at this stage(God forbid) you need to cool them down and fast
best way is immerse them in cold water if you cant do that then hosepipe or pour buckets over them
icecubes on the head can help too and if they are slipping out f consciousness ice near the anus will help too
most important is to cool your dog fast but... if you feel thats not happening get them to the vet fast with wet towels blankets and ice packed around them in the car.
All sounds very scary really but thats how important it is to keep them cool in the first place, I have learned and memorised this from reading many books and searching many websites for the best info
it has never happened to me or anyone I know of here in the UK but just to be safe I always have lemonjuice in my Doggykit.