Mammalia: Nervous System 701 



theme. In these final conscious forms there is nothing of the bewildering 

 complexity of the physical events intervening between orchestra and 

 cochlea and no suggestion of the incredible task performed by the 

 organ of Corti in sorting out the innumerable overlapping sets of vibra- 

 tions and forwarding the resulting stimuli to the brain not only faith- 

 fully but instantly. Heard through such an ear as that of most reptiles, 

 the symphony would probably be, at best, merely a big noise. If dogs, 

 cats, and some human individuals do not enjoy it, the inability is 

 probably more cerebral than auditory. To many a human primate it 

 may be a great esthetic, emotional, and intellectual adventure. 



By use of external means, man achieves not only new sounds for 

 the ear, but new sights for the eye. To the lens of his eye he adds the 

 lenses of his telescopes and microscopes, thereby vastly extending the 

 range of his vision into the far distance of the sky and the near distance 

 of minute things. His cities and objects of art and his written and 

 printed language add bewildering complexity to the "natural" land- 

 scape which confronted his primitive eyes. By photography he sees 

 things which no longer exist and observes events long past — and 

 television has most recently been achieved. 



The senses of smell and taste are less amenable to exploitation 

 than those of sight and hearing. Nevertheless, man's chemical manipu- 

 lation of his environment has produced many new things which may 

 or must be smelled and, by addition of various artificial and syn- 

 thetically produced ingredients, the taste of his natural foods is not 

 always improved but is at least modified, for better or worse. 



Brain 



The assertion that the mammalian brain is relatively large is 

 commonly made — and with the implication that the fact is creditable 

 to the mammal. The significance of size of organs varies according to 

 the nature of their functions. A stomach is large in proportion to the 

 quantity of food it must contain and the amount of digestive fluid it 

 must secrete. A muscle is large in proportion to the power it must 

 produce when it contracts. A heart is large according to the volume of 

 blood it must contain and pump. The size of the constituent cells of an 

 organ does not vary with the size of the organ or animal. Cells of 

 corresponding tissues are of approximately the same size in small and 

 large mammals. (In fact, among amphibians, the largest cells occur in 

 some of the very small salamanders.) In the organs of the larger mam- 

 mals, therefore, the number of cells is correspondingly larger. This is 

 true for the brain, but here the fact has a peculiar significance. 



A suspension-bridge cable is large in diameter because it must 



