Primer on SmellIn addition to bringing out1 the flavor of food, what does the sense of smell do for us ?Smell “gives us information about place, about where we are,” says Randall Reed, a Johns Hopkins University professor whose specialty is the sense of s

Primer on Smell
In addition to bringing out1 the flavor of food, what does the sense of smell do for us ?
Smell “gives us information about place, about where we are,” says Randall Reed, a Johns Hopkins University professor whose specialty is the sense of smell. ___1___ “Whether we realize it or not, we collect a lot of information about who is around us based on smell,” says Reed.
Even at a distance, odors can warn us of2 trouble — spoiled food, leaking gas, or fire. “It’s a great alert,” offers Donald Leopold, a doctor at Johns Hopkins. For example, if something in the oven is burning, everyone in the house knows it.
With just a simple scent, smell can also evoke very intense emotion. Let’s say, for example, that the smell is purple petunias. ___2___ Now let’s imagine that your mother died when you were three, and she used to have a flower garden. You wouldn’t need to identify the smell or to have conscious memories of your mother or her garden. You would feel sad as soon as you smelled that spicy odor.
Compared with3 animals, how well do people detect smelts ?
That depends on what you mean by “how well”. We are low on receptor cells ： current estimates say that humans have roughly five million smell-receptor cells, about as many as a mouse. ___3___
Reed says that, across species, there is a relatively good correlation between the number of receptor cells and how strong the sense of smell is. “You can hardly find the olfactory bulb in a human brain —— it’s a pea-sized object. In a mouse, it’s a little bigger. It’s bean-sized in a rat, about the size of your little finger in a rabbit, and the size of your thumb in a bloodhound.”
Does that mean that our sense of smell is not very acute ?
Not exactly. While we may not have the olfactory range of other creatures, the receptors we do have are as sensitive as those of any animal. ___4___ A trained “nose”, such as that of a professional in the perfume business, can name and distinguish about 10,000 odors. Reed says that a perfume expert can sniff a modem scent that has a hundred different odorants in it, go into the lab, and list the ingredients. “In a modest amount of time, he comes back with what to you or me would smell like a perfect imitation of that perfume. It’s amazing.”
What happens to4 our sense of smell as we age ?
Many people continue to have good olfactory function as they get older. ___5___ Leopold says that smell is generally highest in childhood, stays the same from the teens through the 50s, and drops starting at about 60 for women and 65 for men. “The average 80-year-old is only able to smell things half as well as the average 20-year-old,” says Leopold.

词汇：
scent /sent/ n. 气味，香味
petunia /p 'tju:ni / n. 喇叭花
olfactory / l'f kt( )ri/ adj. 嗔觉的，味道的
sniff /snif/ v. 嗅，闻，用力吸

注释：
1. bring out：使……显出，使……变得明显
2. warn of：发出关于……的警告。warn sb. of sth.：警告某人某事
3. compare with：与……相比
4. happen to：发生于，发生在

练习：
A These flowers have a rich spiciness that no other petunia has.
B Odors, or smells, can warn us about trouble.
C That’s not the rule, however.
D And smell tells us about people.
E We can also think, and we make conscious (and successful) efforts to tell the difference between one smell and another.
F A rat has some 10 million, a rabbit 20 million, and a bloodhound 100 million.