We may here remark that although we are usually able to perceive that the odour and the flavour of a sapid food or drink are akin to each other, the sensation of the odour anticipating that of the flavour, yet they are by no means always identical. They may strike us as do a plain and a coloured version of the same print. Sometimes the flavour seems to be the more powerful, sometimes the odour. Nearly all bouillons, for example, possess a flavour more rich and full than the odour they give off with their steam. On the other hand, valerian has a strong, objectionable smell, which, strange to say, becomes subdued and relatively tolerable when that medicine is being swallowed. It is a curious fact, well known to expert “tasters,” that if the eyes are kept closed during the test, the delicacy of appreciation of flavours, and also of the smell of the wine in the glass, is entirely lost. I cannot suggest any explanation for this curious phenomenon. Anosmia, absence of smell, which is the next topic for our consideration, is a not uncommon defect. It is generally the result of some form of nasal obstruction, such as a bad “cold in the head,” as Æsop’s fox was clever enough to remember. This type is temporary and remediable. But there are other forms that are due to nerve-disease, and for these nothing can be done. A congenital anosmia is occasionally met with, and a curious partial anosmia, reminding us of colour-blindness or tone-deafness. I myself know people who cannot smell coal-gas unless it is very strong, and I once knew a cook,—a cook who couldn’t smell a bad egg! Albinos are said to be congenitally anosmic, and there was recorded many years ago by Hutchison the case of a negro who, gradually losing all his pigment, became anosmic in consequence (cited by Ogle). As the sustentacular cells of the olfactory area contain granules of pigment (see Chapter II.), we are forced to conclude that it must exercise a highly important function in the perception of odours. We shall see later on that its presence is supposed by some to support the theory that odour is a specific ethereal vibration similar to light. We turn now to discuss the real nature of odour, a section of our subject which is still theoretical and highly problematical. Having accomplished so much in the art of perfumery, the chemist ought, one would think, to be able to tell us whether or not there is any relationship or correspondence between odour and chemical constitution.