September 29, 1922] 



SCIENCE 



347 



which the stones hang rather than press, are 

 utilized. These, when any cause inclining the 

 head has passed, hring the head back at once 

 to the normal symmetry of the erect posture. 

 These same bags also manage the posturing of 

 the eyes. The eye contributes to our orienta- 

 tion in space; for example, to perception o£ 

 the vertical. For this the eyeball, that is the 

 retina, has to be postured normally, and the 

 pair of little gravity-bags in the skull, which 

 serve to restore the head posture, act also on 

 the eyeball muscles. Whichever way the head 

 turns, slopes, or is tilted, they adjust the eye- 

 ball's posture compensatingly, so that the 

 retina still looks out upon its world from an 

 approximately normal posture, retaining its 

 old verticals and horizontals. As the head 

 twists to the right the eyeball's visual asis 

 untwists from the right. These reactions of 

 head, eyes and body unconsciously take place 

 when a bird wheels or slants in flight or a 

 pilot stalls or banks his areoplane; and all 

 this works itself involuntarily as a pure 

 mechanism. 



True, in such a glimpse of mechanism what 

 we see mainly is how the machinery starts and 

 what finally comes out of it; of the intei-medi- 

 ate elements of the process we know less. Each 

 insight into mechanism reveals more mechanism 

 still to know. Thus, scarcely was the animal's 

 energy balance in its bearing upon food in- 

 take shown comfortably to conform with 

 thermodynamics than came evidence of the 

 so-called "vitamins" — evidence showing an un- 

 suspected influence on nutrition by elements 

 of diet taken in quantities so small as to make 

 their mere calorie value quite negligible; thus, 

 for the growing rat, to quote Professor Hard- 

 en, a quantity of vitamin A of the order of 

 one flve-hundredths milligram a day has po- 

 tent effect. Again, as regards sex detei-mina- 

 tion, the valued discovery of a visible distinc- 

 tion between the nuclear threads of male and 

 female brings the further complexity that, in 

 such eases, sex extends throughout the whole 

 body to every dividing cell. Again, the assso- 

 ciation of hereditai'y unit-factors, such as body 

 color or shape of wing, to visible details in 

 the segmenting nucleus seemed to simplify by 

 epitomizing. But further insight tends to trace 



the inherited unit chai-acter not to the chromo- 

 some itself, but to balance of action between 

 the chromosome group. As with the atom in 

 this heroic age of physicists, the elementary 

 unit once assumed simple proves, under fur- 

 ther analysis, to be itself complex. Analysis 

 opens a vista of furthei- analysis required. 

 Knowledge of muscle contraction has, from the 

 work of Fletcher and Hopkins on to Hill, Har- 

 tree, Meyerhof and others, advanced recently 

 more than in many decades heretofore. The 

 engineer would find.it difficult to make a mo- 

 tive machine out of white of egg, some dis- 

 solved salts, and thin membrane. Yet this is 

 practically what nature has done in muscle, and 

 obtained a machine of high mechanical effici- 

 ency. Perhaps human ingenuity can learn 

 from it. One feature in the device is alternate 

 development and removal of acidity. The cycle 

 of contraction and relaxation is traced to the 

 production of lactic acid from glycogen and its 

 neutralization chiefly by alkaline proteins; and 

 phyacally to an admirably direct transition 

 from chemical to mechanical effect. What new 

 steps of mechanism all this now opens! 



But knowledge, while making for complexity, 

 makes also for simplification. There seems 

 promise of simplification of the mechanism of 

 reflex action. Reflex action with surprising 

 nicety calls into play just the appropriate 

 muscles, and adjusts them in time and in the 

 suitable grading of their strength of puU. The 

 moderating as well as the driving of muscles 

 is involved. Also the muscles have to pass 

 from the behest of one stimulus to that of an- 

 other, even though the former stimulus still 

 persist. For these gradings, eoadjustments, 

 restraints, and shifts, various separate kinds 

 of mechanism were assumed to exist in the 

 nerve-centers, although of the nature of such 

 mechanisms little could be said. Their pro- 

 cesses were regarded as peculiar to the nerve- 

 centers and different from anything that the 

 simple fibers of nerve-trunks outside the centers 

 can produce. We owe to Lucas and Adrian 

 the demonstration that, without any nerve- 

 center whatever, an excised nerve-trunk with 

 its muscle attached can be brought to yield, 

 besides conduction of nerve impulses, the grad- 

 ing of them. * That is remarkable, because the 



