76 



SCIENCE 



[N. S. Vol. XXVI. No. 655 



would depend upon tlie engineer's ability to 

 distinguish between indistinguisbable signals. 

 As a matter of fact, the reverse of Professor 

 Stratton's statement is true. Instead of being 

 totally, or even partially, color-blind, " the 

 normal eye, grown accustomed to darkness," 

 is much more sensitive to color than is the 

 retina in daylight vision. Indeed, the in- 

 creased color-sensitivity of the dark-adapted 

 retina is so striking and so well-known that it 

 has in several instances been made the object 

 of special investigation. And the investiga- 

 tors who .have made quantitative determina- 

 tions, of this hyperesthesia to color agree that 

 it amounts to, at least, two hundredfold. 



Professor Stratton believes that another rea- 

 son for the misinterpretation of colored signals 

 is to be found in the fact that one " is in- 

 capable of seeing correctly the color of objects 

 caught out of the corner of the eye." He 

 represents the engineer as being so occupied 

 with his engine and his time-piece, that he 

 does not even see his signals until he is upon 

 them. " The color of a signal must be caught 

 in its flight to one side" while the engine 

 rushes past in mad career. It seems unneces- 

 sary to discuss the question as to whether or 

 not Professor Stratton's dramatic description 

 represents the actual procedure adopted by the 

 engineer in the reading of his signals; but it 

 may be remarked that if engineers really do 

 attempt to interpret signals under the condi- 

 tions described by the author, the semaphore 

 device which he advocates would prove to be 

 even more defective than the despised system 

 of colored lights. For while it is true that 

 the outlying regions of the retinal surface are 

 relatively insensitive to color, it is also true 

 that these peripheral regions are even less 

 capable ' of discriminating between spatial 

 forms. 



The author errs again in his discussion of 

 the status of " color weakness." It is popu- 

 larly supposed that there exists a group of 

 individuals who are " weak in their color 

 sense, but by no means color-blind." Pro- 

 fessor Stratton promulgates this erroneous 

 conception, notwithstanding the fact that in 

 an examination of several thousand cases of 



" color weakness " Professor Nagel, of Berlin, 

 found not a single instance of the defect that 

 did not turn out, on closer investigation, to 

 be a familiar case of color-blindness. 



Professor Stratton ' omits to mention that 

 the illuminated semaphore which he recom- 

 mends is an antiquated expedient. It repre- 

 sents an earlier stage in the evolution of the 

 present system of signaling; it was introduced 

 into the railway service many years ago, but, 

 for reasons which need not be discussed here, 

 it never came into general use. Its failure 

 and ultimate supplanting by colored lights are 

 now a matter of history. 



J. W. Baikd 



Univeesitt of Illinois 



the definition of respiration 

 To THE Editor of Science: In the article 

 " On the Teaching of the Subject of Respira- 

 tion " in Science for April 19 it is stated 

 that " the confusion of words is inconvenient 

 enough, but there is back of it a confusion of 

 ideas which is more serious and by which the 

 teaching of the subject is more or less im-^ 

 paired." That this is true there is abundant 

 evidence, while a very superficial glance over 

 the recent literature of the subject shows 

 where the trouble lies. If only one authority 

 were consulted little difficulty would result, for 

 the differences are concerned with words rather 

 than with ideas; each book is clear enough if 

 taken by itself; yet the number of definitions 

 of respiration that are available to the student 

 can lead to nothing but confusion. A few 

 brief quotations will illustrate this. Barnes^ 

 speaks of " another false conception. . . . One 

 often finds respiration described as a gaseous 

 exchange — the taking up of oxygen and giving 

 off of carbon dioxid — a trade between the at- 

 mosphere and the body." More recently Loeb' 

 has stated, " By respiration we mean the 

 taking up of oxygen and the giving off of CO.. 

 We shall see later that the latter process can 

 exist independently of the taking up of oxy- 



' " The Theory of Respiration," Science, Feb- 

 ruary 17, 1905. 



' " The Dynamics of Living Matter," 1906. 



