PROFESSOR AT HEIDELBERG 239 



least some proportion of the visual perceptions to an innate 

 mechanism, in the sense that definite sensations are supposed 

 to set free definite, already formed, spatial conceptions. But 

 the nativistic hypotheses in the first place do not explain 

 anything; they only assume that the fact to be explained 

 exists ; in the second place, the assumption made by all 

 nativistic theories, to wit, that already formed representations 

 of objects are brought out by the organic mechanism, is far 

 more dubious than the assumption of the empiricist theory 

 that it is the raw material of sensations alone which depends 

 on external conditions, while all ideas have to be formed from 

 that in accordance with the laws of thought. In the third 

 place the nativistic assumptions are unnecessary. 1 



Notwithstanding these arguments Helmholtz met with 

 little sympathy even from the best and most sympathetic of 

 the physiologists, who were not only, like du Bois, biased by 

 a certain nativistic tendency, which made them averse to the 

 consistent development of the empiricist hypothesis, but further 

 objected to it on the ground that it did not seem to them 

 compatible with the existence of sensory illusions. Bonders 

 objected to Helmholtz's hypothesis from the same point of 

 view, and received the following answer, dated May 26, 1868 : 



' I regard the publication of careful observations on the 

 mode of vision of people who squint as very desirable and 

 important (provided it is borne in mind that, from the nature 

 of the thing, this may possibly not be constant). The state- 

 ments we have hitherto had about it seem to me to be influenced 

 throughout by preconceived ideas. And although for the time 

 being you are still in the clutches of the nativistic theory, 

 I have sufficient confidence in you (witness your experiments 

 on stereoscopy with electric illumination) to believe that you 

 set facts above theory. For the rest I am well aware that my 

 empiricist theory is at present merely one of the possible 

 aspects of the matter, and that facts may shortly be discovered 

 that will render it impossible : when that happens it will have 

 had its uses, and may disappear. Not indeed that I think this 

 very probable as regards ideas and percepts. As to motor 

 impulses, the case is rather different. Some such are truly and 

 indisputably present in the new-born as much as in the grown 

 person, and the possibility that certain combinations of move- 



