776 



SCIENCE. 



[N. S. Vol. VII. No. 179. 



visual process which was based upon general 

 properties of the nervous substance would be 

 open to the same objection. This is true, and 

 it applies to Miiller's own explanation of the 

 phenomenon in question with peculiar force. 

 But the conclusion to be drawn is not that one 

 visual theory is sure to be just as good as 

 another, but rather that that theory which 

 posits a chemical process which is not exactly 

 like what goes on everywhere else in the body 

 has by so much the advantage over another 

 theory. The idea of a photo-chemical sub- 

 stance which is unstable after a partial dissocia- 

 tion, which it is as far as possible from being a 

 remote idea to the chemist, is just as far re- 

 moved from our conception of other physiolog- 

 ical processes as it must he, in a well-devised 

 theorjf, in order to account for anything so ex- 

 tremely distinctive as is the visual after-image. 



But even though it had been necessary to go 

 very far afield for the conception of a semi-sui- 

 cidal chemical substance, this could not have 

 been counted, by any one who had given a mo- 

 ment's consideration to the subject, as a point 

 of superiority on the part of Hering's theory 

 over mine ; for his assumed photo-chemical 

 substance is ' suicidal' from the start. If blue 

 ■is the color of assimilation, then after we have 

 looked at a blue surface for a few moments 

 there has been piled up in the retina, according 

 to Hering, a large amount of the blue-j'ellow 

 substance, and it is the going to pieces of this 

 immediately afterwards which is the cause of 

 the after-image ; this assumed process is not 

 in itself an objection to the theory, but it is 

 ' suicidal' to the last degree. 



Professor Miiller's recent papers in the Zeit- 

 sehriftfur Psychologie are a monument of learn- 

 ing and acumen, as I have already said in the 

 pages of The Psychological Review. How far 

 they are from substituting for the original 

 theory of Hering a theory which can lay any 

 claim whatever to being considered an adequate 

 account of the phenomena of color-vision I am 

 about to show in connection with a general dis- 

 .cussion of color theories. Meantime I rejoice 

 in the fact that Professor Titchener has renewed 

 his study of the subject of color. It is to be 

 hoped that this will lead him to remodel the 

 brief statements regarding color which are found 



in his book on Psychology ; what he says there 

 (while it is not incomprehensible to one who has 

 the clue to his secret meaning) must seem con- 

 tradictory and confusing in the extreme to the 

 ordinary reader, and certainly constitutes a 

 serious blemish in a book which is otherwise 

 not simply a good text-book, but a valuable 

 contribution to the science of psychology. 



C. Ladd Franklin. 

 Baltimore. 



a precise criterion of species. 

 To THE Editor of Science : I thank you for 

 the suggestions contained in your kind discus- 

 sion in Science, No. 178, of Mr. Blankinship's 

 and my paper on a ' Precise Criterion of 

 Species.' Our paper was concerned with a 

 method which, if applied, will constitute a 

 small, but, we think, important, step toward 

 giving greater precision to the defining of par- 

 ticular species and to the distinguishing of 

 varieties from species. To my mind the only 

 important objection urged so far, an objection 

 which was anticipated, is that it is impractica- 

 ble to use in systematic work so great precision 

 as our method calls for ; it takes too much time 

 and too large a number of individuals. A 

 priori argumentation cannot dispose of this for- 

 midable objection ; only the demonstrated ad- 

 vantage of the method in practice can avail 

 against it. I should like to urge anthropolo- 

 gists, mammalogists, ornithologists, ichthyol- 

 ogists, malacologists and others who have al- 

 ready gone some way in the direction of 

 applying statistics to species to put the method 

 to practical test. Mr. Blankinship and I are 

 doing so. I should be very glad to assist those 

 who meet with difficulties in the application of 

 the method, as, for example, in the measure- 

 ment of color and complex forms. The inge- 

 nious naturalist will find, however, as anthro- 

 pologists have found, few, if any, specific 

 difiPerentiDe which are not measurable. 



C. B. Davenport. 



electrical anaesthesia. 



To THE Editor of Science : While making 



some experiments on the sensations derived 



from sinusoidal currents I noticed (April 12, 



1898) that ansesthesia of the tissues resulted 



