August 22, 1890.] 



SCIENCE. 



lOI 



a second, or a duration of SSff to 25ff. For sound, different 

 observers have chosen different points for measurement. 

 The slowest rate of impressions fusing into a musical sound 

 has been fixed at between 30 and 40 per second ; but Helmholtz 

 has shown that the interference of sound-waves perceptible 

 as beats does not escape detection when recurring as rapidly 

 as 132 per second. For non-musical sounds, such as electric 

 clicks, a still higher rate has been found. In touch we dis- 

 tinguish differences of feeling when impressions are rapid 

 enough to fuse but not rapid enough to fuse perfectly. The 

 smoothness of a polished surface is not obtained until the 

 impressions occur 480 to 640 times a second (Valentin). For 

 taste and smell the period, though not accurately determined, 

 is undoubtedly very long. Here the time needed to reach 

 the somewhat concealed sense-organs is considerable, and the 

 chemical processes involved are relatively slow in action. 

 The influence of the mode of activity of the sense-organ upon 

 its period of stimulation is further illustrated in the long 

 inertia period of the probably chemical action of vision com- 

 pared with the short period of the mechanical senses of hear- 

 ing and touch. This view is also supported by the fact that 

 the period for the retina is shortened if the eye be directly 

 stimulated electrically. Another mode of experimenting 

 consists .in applying a stimulus for the minimum time during 

 which it can be recognized. The time thus measured will be 

 shorter than the other, for it tells us only liow long is needed 

 for initiating the process of recognition sufficiently to have 

 it continue to completion (probably after the stimulus ceases). 

 This is indeed a surprisingly short time. Cattell and San- 

 ford independently found that a color or a letter could be 

 recognized when visible for only from Iff to 5ff, while less 

 recently Bast recognized 6 to 7 letters when exposed for only 

 5(7. Others have calculated that the ma.ximum effect of an 

 impression is not reached until from SOff to ISOff, but these 

 determinations seem to involve some mental process of recog- 

 nition. Whether or not some such process of recognition is 

 involved is not quite clear. Unless specially prevented, the 

 recognition will take place on the basis of the after-image, a 

 few thousandths of a second being sufBcient to initiate the 

 process. By following the impression by a strong flash of 

 light, and thus nullifying the after-image, Baxt found a 

 longer time needed to recognize a more complicated impres- 

 sion. Within 10(T to 15(7, one letter : within 24(7, three letters ; 

 within 34(7, four letters, could he recognized. This only 

 partially excludes the effect of the after-image, so that per- 

 haps the results with complicated impressions are minimum 

 " recognition times," and those with simple impressions 

 '■ inertia times." Another method, that of Exuer, is similar 

 to the method of fusion. It consists in flnding how closely 

 two impressions, stimulating slightly different portions of 

 the sense-organ, may follow one another and yet be recog- 

 nized as successive. Optical impressions were so recognized 

 when falling at an interval of 44(7 on two points of the retina 

 near the centre .011 millimetres apart, a longer time being 

 necessary if the points are away from the centre of the ret- 

 ina. It seems probable that this process is more complicated 

 than the one we are attempting to study. While the data 

 thus at our disposal do not allow us to fix accurately the 

 time of sensory inertia, the estimate provisionally accepted 

 in the text cannot be far from the truth, being rather over 

 than under estimated. The methods of measuring the rate 

 of nervous impulses (b) and (c) have already been described. 

 The inertia of the muscle and the time of its contraction are 

 determined upon the same apparatus by observing how much 

 after the shock is given the curve leaves the base-line. 

 Reflex, Automatic, and Voluntary Re-actions. 

 The term " re-action " as here used is not intended to in- 

 clude all responses to stimuli. The above instanced forms 

 of reactions present various grades of naturalness, utility, 

 and habituation ; that is, the association between motion and 

 stimulus has by practice hecome more or less close and easy. 

 Copying, for example, may become so entirely automatic 



that it runs on of itself without the need of renewed voli- 

 tional effort. The actions recognized as reflex take place in 

 spite of all volition. The re-actions here considered are 

 limited to those requiring some degree of voluntary effort for 

 their execution, though this may be almost indefinitely re- 

 duced by practice. The reflex act takes very much less time 

 for its execution than the voluntary : the time for winking 

 has been determined by Exner to be something over 50(7. 

 In other words, it takes about three times as long to signal 

 by a voluntary closixre of the eye-lid that an impression has 

 been received as to perform the same act reflexly when 

 the eye is threatened. The utility of this quick action for 

 the protection of the eye is evident; and other useful re-ac- 

 tions, such as those of flight and escape in timid animals, 

 seem to be of a similar nature. The quick movements of 

 defence when attacked, of regaining one's balance when slip- 

 ping, are so immediately useful and so well inculcated in 

 the organism as often to surprise us by their quickness. 

 Most of these actions can also be performed voluntarily, but 

 neither so well nor so quickly ; it is therefore diificult to 

 subject them to experiment. As already indicated, in the 

 ordinary re-action there is little naturalness in the connec- 

 tion of stimulus and movement, the same type of movement 

 being used for all. The experienced re-actor becomes accus- 

 tomed to signal by the finger movement that the operation 

 required of him has been accomplished, but hardly associ- 

 ates this movement with any particular stimulus. 



It is perhaps well to add that the great saving of time in 

 actions that have become automatic (such as is seen in the 

 experienced piano player or post-office clerk as compared 

 with the beginner), is in great part due to the increased 

 facility of doing several things at once and not serially, a 

 factor that enters only in a small degree into the simple re- 

 action. The processes we should he most interested in 

 measuring are those most closely approaching the operations 

 of daily thought, so that the inference from experiment to 

 practice shall be as direct as possible. This, however, it is 

 difficult to do, because every-day mental processes do not 

 present the simplicity of conditions required by experiment. 

 Accordingly the method has been to study the simplest re- 

 actions, and then take into account the circumstances in 

 which our usual mental operations differ from them. 



[To be continued.] JOSEPH JaSTROW. 



LEGISLATION ON FOOD ADULTERATION. 



The adulteration of alimentary substances has been prac- 

 tised from the most ancient times, and numerous laws and 

 regulations have been adopted in various countries to check 

 and prohibit such sophistications.' 



France has taken the lead in protecting consumers of food 

 from adulterations, and in 1802 the Coaseil de Salubrite was 

 established in Paris. In England as well as in France, 

 Germany, and other Continental countries, laws against the 

 adulteration of individual articles, such as tea, coffee, beer, 

 and wine have been passed since the middle ages. The first 

 general act was not passed in England till 1860, and this was 

 amended in 1872. However, they were found unsatisfac- 

 tory, and the Sale of Food and Drugs Act was passed in 

 1875, and further amended in 1879 in the endeavor to obtain 



1 For copies of European laws on food adulteration see Report of the Com- 

 missioner of Internal Revenue for 1888 and for 1889; and for a summary of 

 their leading features see Science, siv., p. 308. 



