THE PHYSIOLOGY OF THE SPECIAL SENSES. 145 



impressions of one sense by those of another. Hence, if we are 

 to do good work, we must be extremely careful to distinguish 

 between what we see and what we think we see. And it is of the 

 greatest value, when looking at an object under the microscope, to 

 write down a description of it without using any technical words 

 whatever, merely describing the objects as dark and light patches, 

 or areas, giving their size with the micrometer, and describing the 

 shape of their outline, etc., together with any other physical 

 details; and, afterwards, to write down what we infer from these 

 details as to their possible structure and nature. For it is surpris- 

 ing how often we are led unconsciously to see what we want to see, 

 and how grossly we can voluntarily deceive our senses, 



I will endeavour to prove my statement in the case of all of 

 you here to-night by a very simple experiment. If I take this 

 tumbler standing on the table, you see it is upright; if I now tilt 

 it slightly, the rim at the top is in the reverse position to you. 

 Now, if you will close one eye or half-shut both, you can see the 

 rim in the tilted position — that is, the proximal edge of the rim is 

 now the distant edge, although you know perfectly well that it 

 could not stand in such a position.''' With a little practice you can 

 do this with the eyes wide open. Seeing, then, how easily we can 

 deceive ourselves voluntarily, and how much more easily we may 

 be deceived unconsciously, it behoves us to proceed very cautiously 

 in using an instrument like the microscope, and to make as certain 

 as possible that our data are accurate before we proceed to draw 

 our conclusions. 



The association between stimuli and mental pictures is so close 

 and remains so long, that often a sudden stimulus, similar to one 

 received many years before, may bring back the whole mental 

 picture with extreme vividness. This is especially the case with 

 the sense of smell. The slightest stimulus of the organ of smell, 

 not even sufficient to be noticeable to us as distinct, may bring 

 back some long-forgotten scene, whilst we puzzle over what could 

 have made us think of it. And I may here note by the way that 

 in man the sense of smell is apparently to a great extent a lost 

 sense. It is not nearly so highly developed as in the lower 



* I am indebted for this experiment to Mr. Waller; a full description can be 

 found in his Human Physiology^ p. 542, published by Longmans and Co. 



