36

ment (Fig. 72) the water in a bowl was heated by means of a little flame under the bulb which communicated with the bowl by a tube; the temperature rose at the rate of 0.002° C (10% of a degree Fahrenheit) per second as indicated by a thermometer in the bowl. The frog never moved and at the end of two and one half hours was found dead. He

had evidently been

boiled without noticing it.

There is a curi

FIG. 72.-Boiling a Frog without His Knowing it.

Rate of Change.

ous connection be- No Sensation with an Extremely Slow tween temperature and pressure. Cold or hot bodies feel heavier than bodies of equal weight at the temperature of the skin. For cold, take two silver dollars; keep one of them closed in the hand to give it the temperature of the skin, but cool the other. Apply them in succession to the palm of some one's hand. The cold one will seem much heavier. Heat does not make so much difference as cold. For a careful experiment take two wooden cylinders of equal weight and heat one very hot in an oven. Apply the cylinders on end to the back of the hand. This phenomenon illustrates the fact that a sensation of one kind often causes an apparent increase in the strength of another sensation.

CHAPTER X

SMELL AND TASTE

N spite of the antiquity of language, we have no

taste.

name it by the source from which it comes. We speak of the odour of violets, of new-mown hay, of onions, and so on, but we have no name for the odour itself. Such a lack is not present in sight, hearing, or even We might say that certain things taste like sugar, certain others like quinine, and so on; but that would be only a roundabout way of saying they were "sweet" or "b.tter." Instead of classifying the colours, as grass colour, dandelion colour, coal colour, etc., we say green, yellow, black, etc. But in smell we can only speak of cabbage odour, fishy odour, violet odour, and the like.

Not only do we have no names for odours, we do not know any reason why different things smell alike. Why should compounds of arsenic smell like garlic? If we mix sulphuric acid with water, we get an odour like musk. It is said that emeralds, rubies, and pearls, if ground together for a long time, give out an odour like that of violets. Again, ringworm of the scalp, the body of a patient sick with typhoid, and a mouse have similar odours.

Perfumes can often be placed in similar groups. The rose type includes geranium, eglantine, and violetebony; the jasmine type, lily of the valley and ylangylang; the orange type, acacia, syringa, and orangeflower; the vanilla type, balsam of Peru, benzoin, storax, tonka bean (usually sold for vanilla extract), and heliotrope; the lavender type, thyme and marjoram; the mint type, peppermint, balsam, and sage; the musk type, musk and amber seed; the fruity type, pear, apple, pine-apple, and quince.

What is the threshold of smell? There is a convenient but not highly accurate way of answering the question by means of the olfactometer, or smell

measure.

The olfactometer (Fig. 73) includes a glass tube fastened on a narrow board. Inside this tube

is a narrow strip of blotting-paper mois

tened with the object to be smelled. A solution of camphor in alcohol is convenient; the solution dries, leaving the strip filled with small particles of camphor. Any other not too odorous liquid may take the place of the camphor solution. Inside the tube is a smaller one on the end of which is a piece of rubber tubing. A scale is marked on the board below the tubes.

The end of the smaller tube is pushed to the end of

the larger one. The old air in it is blown out. The rubber tube is put to the nose. The smaller tube is now slowly drawn backward, while the person breathes air in through it. When he first perceives an odour, the distance through which the smaller tube has been drawn from the end of the larger one, is noted. Now, the further the tube is drawn back, the greater the distance over the blotter travelled by the air breathed; consequently there is more of the camphor in the air. The number thus noted down gives an idea, though not a very accurate one, of the person's threshold of smell.

In the whole range of psychology there is nowhere to be found a more striking method of illustrating the difference between the different thresholds of knowledge. As the smelling-tube is pulled backward the observer at first notices no odour; the odour is said to be below the threshold. After a while he says: "I smell something, but I can't tell what it is"; a sensation is there, it is known as an odour, it has passed the "threshold of sensation," but has not reached the "threshold of recognition" (if I may use such an expression). The odour becomes stronger and stronger; finally the observer exclaims, "Now I know the odour; let me think a moment and I will tell you the name." Very frequently he recognises the odour without being able to recollect the name. The difference between the threshold of sensation and the threshold of recognition is often considerable. If the odour is still further increased, the name, for usual substances, is readily recollected.

Our sense of smell can be fatigued. Holding a piece

of camphor for some minutes before the nose will raise the threshold for camphor. With an olfactometer charged with camphor the threshold as measured before fatiguing the sense of smell will be found to be much lower than the threshold afterwards. Sometimes the fatigue is so great that the smell of the camphor is entirely lost. Strangely enough the fatigue affects some odours and not others. If the sense be affected by camphor-fatigue, the smell of wax will be diminished or lost, but essence of cloves will appear undiminished in strength.

We have two senses of smell, namely, the two halves of the nose. When two different smells are received, one from each organ, we are driven to notice first one, then the other. When a rose is placed in one paper tube (Fig. 74) and a water-lily in another and the tubes are so arranged that the odours get to separate nostrils without mix. ing, we do not smell a combination, but alternately either rose or water-lily. We can smell either one in preference to the other by simply thinking about it (compare p. 21).

It

FIG. 74.-Alternation of Odours; or the
Strife of the Two Nostrils.

is a very curious fact that we are unable to think of the same odour steadily; our thoughts irresistibly turn from one to the other and thus the smells alternate.