THE NOSE. 189 



themselves to the eyes of the animal, it appears as thou2;Ii 

 care was taken, that he should have the means of principally 

 collecting such only as are connected with his views or pur- 

 suits. The form of the visual organ is such that no con- 

 fusion exists from an indiscriminate admission of rays ; thus 

 only such enter as are suited to this convergency ; or, if 

 any others do penetrate, they become lost in the pigmen- 

 tum nigrum. It is therefore to be understood that the rays 

 which the refracting power of the humours is able to con- 

 centrate, meet upon the retina in a point ; or in a very small 

 circle, within which the object is painted ; and that the mind 

 takes cognizance of it through the medium of the optic 

 nerves. As the eye must necessarily require to have avast 

 variety of objects painted upon it, whose distances are 

 widely different ; so there must be some optical adjustment 

 of the powers of the part, to enable it to effect a distinct 

 vision of all objects remote or near. On this subject we have 

 first to consider that the outer coat of the eye is formed of 

 a yielding material ; such as is disposed to be moulded into 

 a variety of shapes, by the pressure of the muscles which sur- 

 round it. The eye likewise, not being fixed in its place, is 

 likely to be retracted, or drawn back, by the muscle specially 

 formed for this purpose ; as well as to be urged forward by 

 the pressure of the fat behind the organ. Were it not for 

 some adjustment of the optical organs, the rays reflected 

 from objects very near the eye would fall behind it ; and 

 those from very distant ones would, from being almost 

 parallel, meet together before the retina. The mechanical 

 adjustment of the focus, it must be observed, is also assisted 

 by the iris ; which lessening the opening of the pupil when 

 we look at minute objects, only permits such rays to pass 

 as penetrate towards the centre of the lens ; by which they 

 will be very much refracted ; but when the eye regards dis- 

 tant objects, the iris becomes dilated ; and the rays are then 

 received through the edges of the lens, whereby their refrac- 

 tion is diminished. 



THE NOSE. 



In brute animals, the organ of smelling is most essential ; 

 as it forms one of the means by which they judge of good 

 or evil : consequently we cannot be surprised that the nose 



