Ill] OF PAKTS OR ORGANS 91 



The second part of the table shews the steadily decreasing 

 weights of the organs in question as compared with the body; 

 the brain falling from over 12 per cent, at birth to little over 

 2 per cent, at five and twenty; the heart from -75 to -46 per 

 cent. ; and the hver from 4-57 to 2-75 per cent, of the whole 

 bodily weight. 



It is plain, then, that there is no simple and direct relation, 

 holding good throughout life, between the size of the body as a 

 whole and that of the organs we have just discussed; and the 

 changing ratio of magnitude is especially marked in the case of 

 the brain, which, as we have just seen, constitutes about one-eighth 

 of the whole bodily weight at birth, and but one-fiftieth at five 

 and twenty. The same change of ratio is observed in other 

 animals, in equal or even greater degree. For instance. Max 

 Weber* tells us that in the Hon, at five weeks, four months, 

 eleven months, and lastly when full-grown, the brain-weight 

 represents the following fractions of the weight of the whole 

 body, viz. 1/18, 1/80, 1/184, and 1/546. And KelHcott has, in 

 hke manner, shewn that in the dogfish, while some organs (e.g. 

 rectal gland, pancreas, etc.) increase steadily and very nearly 

 proportionately to the body as a whole, the brain, and some other 

 organs also, grow in a diminishing ratio, which is capable of 

 representation, approximately, by a logarithmic curve f. 



But if we confine ourselves to the adult, then, as Raymond 

 Pearl has shewn in the case of man, the relation of brain-weight 

 to age, to stature, or to weight, becomes a comparatively simple 

 one, and rnay be sensibly expressed by a straight line, or simple 

 equation. 



Thus, if W be the brain-weight (in grammes), and A be the 

 age, or S the stature, of the individual, then (in the case of Swedish 

 males) the following simple equations suffice to give the required 

 ratios : 



W = 1487-8 - 1-94^ = 915-06 -f 2-86 iS. 



* Die Sdugethiere, p. 117. 



t Amer. J. of Anatomy, vm, pp. 319-353, 1908. Donaldson {Journ. Camp. 

 Neur. and Psychol, xvm, pp. 345-392, 1908) also gives a logarithmic formula for 

 brain-weight (y) as compared with body-weight (x), which in the case of the white 

 rat is J, = -554 -^ -569 log (a;— 8-7), and the agreement is very close. But the 

 formula i& admittedly empinca and as Raymond Pearl says (Amer. Nat. 1909, 

 p. 303), " no ulterior biological significance is to be attached to it." 



