57 



SCIENTIFIC SIDE-LIGHTS 



Atoms 

 Attenuation 



283. ATTENTION BRIEF IF VOLUN- 

 TARY Longer Sustained if Passive Con- 

 stant Change of Object Variety Needed. 

 There is no such thing as voluntary atten- 

 tion sustained for more than a few seconds 

 at a time. What is called sustained volun- 

 tary attention is a repetition of successive 

 efforts which bring back the topic to the 

 mind. The topic once brought back, if a 

 congenial one, develops ; and. if its develop- 

 ment is interesting it engages the attention 

 passively for a time. . . . This passive 

 interest may be short or long. As soon as 

 it flags, the attention is diverted by some 

 irrelevant thing, and then a voluntary ef- 

 fort may bring it back to the topic again; 

 and so on, under favorable conditions, for 

 hours together. During all this time, how- 

 ever, note that it is not an identical object 

 in the psychological sense, but a succession 

 of mutually related objects, forming an 

 identical topic only, upon which the atten- 

 tion is fixed. No one can possibly attend 

 continuously to an object that does not 

 change. JAMES Psychology, vol. i, ch. 11, 

 p. 420. (H. H. & Co., 1899.) 



284. ATTENTION, FIXATION OF 



The Microscopist's Purposed Blindness. 

 The practised microscopist, whilst apply- 

 ing one of his eyes to his instrument, and 

 determinedly giving his whole attention to 

 the visual picture he receives through it, 

 can keep his other eye open without being 

 in the least disturbed by the picture of the 

 objects on the table, which must be formed 

 upon its retina, but which he does not see 

 unless their brightness should make him 

 perceive them. CARPENTER Mental Physi- 

 ology, ch. 3, p. 135. (A., 1900.) 



285. ATTENTION IN LISTENING 



Ability to Fix on Particular Part in a Har- 

 mony. In the act of listening we are not 

 only distinctly conscious of sounds so 

 faint that they would not excite our notice 

 but for the volitional direction of the atten- 

 tion, but we can single out these from the 

 midst of others by a determined and sus- 

 tained effort, which may even make us 

 quite unconscious of the rest so long as 

 that effort is kept up. Thus a person with 

 a practised " musical ear " ( as it is com- 

 monly but erroneously termed, it being not 

 the ear, but the brain, which exerts this 

 power), whilst listening to a piece of music 

 played by a large orchestra, can single out 

 any one part in the harmony and follow it 

 through all its mazes; or can distinguish 

 the sound of the weakest instrument in the 

 whole band and follow its strain through 

 the whole performance. And an experi- 

 enced conductor will not only distinguish 

 when some instrumentalist is playing out of 

 tune, but will at once single out the of- 

 fender from the midst of a numerous band. 

 CARPENTER Mental Physiology, ch. 3, p. 

 137. (A., 1900.) 



286. ATTENTION, POWER OF, AT- 

 TRIBUTED TO EARTHWORMS Apparent 

 Evidence of Mental Preoccupation. When 

 a worm is suddenly illuminated and dashes 

 like a rabbit into a burrow to use the 

 expression employed by a friend we are at 

 first led to look at the action as a reflex 

 one. The irritation of the cerebral ganglia 

 appears to cause certain muscles to contract 

 in an inevitable manner, independently of 

 the will or consciousness of the animal, as 

 if it were an automaton. Bufc-th different 

 effect which a light produced on different 

 occasions, and especially the fact that a 

 worm when in any way employed and in 

 the intervals of such employment, whatever 

 set of muscles and ganglia may then have 

 been brought into play, is often regardless of 

 light, are opposed to the view of the sudden 

 withdrawal being a simple reflex action. 

 With the higher animals, when close atten- 

 tion to some object leads to the disregard of 

 the impressions which other objects must be 

 producing on them, we attribute this to 

 their attention being then absorbed; and 

 attention implies the presence of a mind. 

 Every sportsman knows that he can ap- 

 proach animals whilst they are grazing, 

 fighting, or courting, much more easily than 

 at other times. The state, also, of the 

 nervous system of the higher animals dif- 

 fers much at different times; for instance, 

 a horse is much more readily startled at one 

 time than at another. The comparison here 

 implied between the actions of one of the 

 higher animals and of one so low in the 

 scale as an earthworm may appear far- 

 fetched, for we thus attribute to the worm 

 attention and some mental power; never- 

 theless I can see no reason to doubt the 

 justice of the comparison. DARWIN For- 

 mation of Vegetable Mould, ch. 1, p. 7. 

 (Hum., 1887.) 



287. ATTENUATION OF VIRULENCE 

 OF BACTERIA Pasteur's Method Protection 

 by Weakening the Enemy. It was pointed 

 out by some of the pioneer bacteriologists 

 that the function of bacteria suffered under 

 certain circumstances a marked diminu- 

 tion in power. Later workers found that 

 such a change might be artificially pro- 

 duced. Pasteur introduced the first 

 method, which was the simple one of allow- 

 ing cultures to grow old before subcultur- 

 ing. Obviously a pure culture cannot last 

 forever. To maintain the species in char- 

 acteristic condition it is necessary fre- 

 quently to subculture upon fresh media. 

 If this simple operation be postponed as 

 long as possible consistent with vitality, and 

 then performed, it will be found that the 

 subculture is attenuated, i. e., weakened. 

 Another mode is to raise the pure culture 

 to a temperature approaching its thermal 

 death-point. A third way of securing the 

 same end is to place it under disadvantage- 

 ous external circumstances, for example a 

 too alkaline or too acid medium. A fourth, 



