14 



SCIENCE. 



[Vol. XV. No. 361 



LETTERS TO THE EDITOR. 



*^*Correspondents are requesiedtobe as brief as possible, Tke writer's name is 

 in allcases required as proof o/ good faith. 



Tke editor will be glad to publish any queries consonant with the character of 

 ike journal. 



On request^ twenty copies of the number containing his communication will be 

 furnished free to any correspondent. 



Unconscious Bias in Walking. 



The question is again raised as to the cause of the deviations 

 from a right line in walking with the eyes closed, or in the dark, in 

 the letter to the editor with the caption " Is Man Left-Legged " 

 {^Science, xiv. p. 412). Several theories have been advanced to ac- 

 count for the frequently observed phenomena referred to, which 

 may be briefly stated as follows : — 



1. The legs are not of equal strength, and the strongest outwalks 

 the other, making a curve to the opposite side. 



2. The relative dexterity with which the legs are used ; some 

 persons being right-legged, and others left-legged, regardless of 

 strength or' length. It is probable, however, that there will be the 

 greatest dexterity with the strongest limb ; and, if so, this is only 

 another form of the first theory. 



3. The legs are not of equal length, and a person will take the 

 longest step wztk the longest leg. 



4. The legs are not of equal length, and a person will take the 

 longest step_/roOT the longest leg. 



In the last two theories, it will be observed, opposite conclusions 

 are reached from the same assumed facts. 



Several years ago I made a careful series of experiments with 

 forty-nine young men to test the correctness of these theories. Their 

 legs were accurately measured to determine the length, and a dy- 

 namometer was used to ascertain the relative strength. The curves 

 representing their bias in walking when blindfolded were accu- 

 rately traced and plotted on a diagram, so that they could be 

 readily compared and studied. 



The results of these experiments (published in Nature, July 30, 

 1885) were as follows : Of five cases in which there was no bias, in 

 two the right leg was longest (in one of these the right leg was 

 strongest, and in one the strength of the legs was not tested), — one 

 presented the greatest difference in length of legs, and the other 

 more than the] average of those with right leg longest, — and in 

 three the legs were of equal length (in one of these the right leg 

 was strongest, and in two the left leg was strongest (a)). Four 

 were right-handed : one used right and left with equal dexterity {a). 

 In pointing at a distant object with both eyes open, in three the 

 right eye was dominant, in one the left eye was dominant, and in 

 one both eyes were apparently used to determine the range. Of 

 fourteen cases in which the bias was to the right, in five the right 

 leg was longest (in two the right leg was strongest, in two the left 

 leg was strongest, and in one the strength of the legs was not 

 tested), in four the left leg was longest (in three the right leg was 

 strongest {a), and in one the left leg was strongest), and in five the 

 legs were of equal length (in two the right leg was strongest {a), 

 and in three the left leg was strongest). All were right-handed. 

 In pointing at a distant object with both eyes open, in twelve the 

 right eye was dominant, and in two the left eye was dominant, the 

 latter in the groups marked (a). Of thirty cases in which the bias 

 was to the left, in eight the right leg was longest (in five the right 

 leg was strongest {a) (b), in two the left leg was strongest, and in 

 one the legs were of equal strength), in ten the left leg was longest 

 (in five the right leg was strongest {b), in four the left leg was 

 strongest {b), and in one the legs were of equal strength), and in 

 twelve the legs were of equal length (in five the right leg was 

 strongest, in five the left leg was strongest {b), and in two the 

 strength of the legs was not tested). One was left-handed {a), 

 twenty-five were right-handed, four used right and left with nearly 

 equal dexterity {b). In pointing with the finger at a distant object 

 with both eyes open, in twenty-two the right eye was dominant, in 

 six the left eye was dominant, and in two both eyes were appar- 

 ently used to determine the range. 



From the facts here presented, it is evident that the relative 

 length or strength of the legs cannot be assigned as the cause of 



the observed bias in walking. The phenomena in question can, 

 however, be readily explained by the application of well-established 

 physiological principles. 



When walking in a straight line, the muscles of locomotion are 

 made to act in orderly correlation through impressions received by 

 the senses and conveyed to the nervous centres, and thence trans- 

 mitted to the muscles by the motor nerves. 



When a person is blindfolded, or in the dark, or in a mist, the 

 senses cannot serve as guides to direction, and the muscles of the 

 two sides of the body may not act with the same energy, from dif- 

 ferences in nutrition, or from lack of co-ordinating impulses from 

 the nervous centres ; that is to say, an exact equilibrium in the 

 muscular activity of the two sides of the body can only be secured 

 through the co-ordinating influence of the senses acting through 

 the nervous system. When this directive agency is not available, a 

 divergence from a direct course will, in most cases, follow from a 

 lack of bilateral symmetry in the functional activity of the muscles. 



Manly Miles. 



Lansing, Mich., Dec. 26. 



The Influence of Baking-Powder Residues on Digestion. 



There has always been more or less discussion over the ques- 

 tion of what a pure baking-powder should consist, and which of 

 the constituents of many kinds of baking-powders are most delete- 

 rious to the human system. 



The manufacturers of different brands of powders obtain in- 

 dorsements from eminent chemists that theirs is the only powder 

 on the market which does not exert a harmful effect when taken 

 every day in our food. 



What one manufacturer calls an adulteration another claims is 

 beneficial to the health, when taken in small quantities. This is 

 especially true in the case of the animated discussion in the news- 

 papers at the present time between the manufacturers of the vari- 

 ous phosphate baking-powders and those who produce a powder 

 made of bicarbonate of soda and cream-of-tartar. 



The manufacturers of the latter brands advertise that theirs 

 does not contain any calcium phosphate, and look upon this com- 

 pound as an adulterant ; while the firms interested in the sale of 

 the former brands laud the use of phosphates in food, at the same 

 time claiming that the bicarbonate of soda and cream-of-tartar form, 

 after baking, a residue of Rochelle salts, the constant introduction 

 of which daily into the stomach would prove very deleterious to 

 the action of the gastric juice. 



While these claims are made by the different manufacturers 

 merely for the purpose of selling their own goods, and conse- 

 quently the harmfulness of their rivals' products greatly overdrawn, 

 yet in a measure the claims of both are true. 



That all baking-powders have, to a greater or less degree, a re- 

 tarding action on digestion by reason of the difficultly soluble salts 

 left as residues after the process of baking, no one doubts ; but 

 now the question arises, " Which of the constituents used in the 

 manufacture of baking-powders have the least injurious effects .' " 



In order to learn what were the most common adulterants of 

 baking-powders, the writer made a tour of many grocery- stores in 

 the city of New Haven, and was enabled to purchase thirteen dif- 

 ferent brands. In all cases it was found that the cheaper brands, 

 and those offering inducements to [the poorer classes by reason of 

 their gifts of household articles, etc., with the purchase of their 

 powders, were adulterated to by far the greatest extent. 



The adulterations in some of these cases were not of a harmful 

 character in themselves; e.g., starch was used in a very liberal 

 quantity on account of its being so much cheaper than bicarbonate 

 of soda and cream-of-tartar. 



The only ill effect produced by the use of starch is, that, the 

 strength of the powder being lessened so much by the absence of 

 the proper amount of bicarbonate of soda, the housekeeper is forced 

 to use a great quantity of the powder in order to cause the libera- 

 tion of carbonic-acid gas necessary for the lightness of the bread 

 or pastry. Thus the stomach gets a greater dose of impurities, 

 which generally occur in a powder adulterated with starch, than it 

 would from a powder not containing the latter ingredient. 



