HELMHOLTZ IN KONIGSBERG 



he could make them shine, an experiment very easily 

 repeated. Then came Helmholtz, who went deeper 

 into the subject, and invented the instrument. It 

 will be seen how true it was that Briicke came near 

 the invention, but still there is all the difference in 

 the world between doing a thing and not doing it. 

 The first account of the ophthalmoscope was pub- 

 lished in 1851. J 



In his great work on physiological optics, the first 

 part of which was published in 1856, Helmholtz 

 gives a full account of the whole subject, and as it is 

 of extreme interest to medical men, I shall take the 

 liberty of making full use or it, sometimes using his 

 own words. 



Light from the eye has been observed from early 

 times coming from the eyes of dogs, cats and other 

 animals who had a tapetum in the fundus of the eye 

 that is to say, an area devoid of pigment, and covered 

 with thin and highly-reflecting fibres. In these animals 

 the reflection is so intense as to be easily perceived, 

 even in unfavourable circumstances. The ancient 

 and prevalent opinion was that those luminous eyes 

 developed light, and that when the animals were 

 irritated, light was evolved from their eyes under the 

 influence of their nervous system. As the light of 

 the eyes is best recognised when the light comes 

 from behind the observer and skims over his head, it 



1 Beschreibung ernes Augenspiegeh -zur Untersuchung der Net%haut in 

 lebenden Auge. Berlin, 1851. 



75 



