196 COLOR-BLINDNESS : CHAPTER XIX. holmgren’s method op testing. — examina¬ tion AND DIAGNOSIS. Justice to Professor Holmgren demands that I should here explain what he has done in reference to these various forms or methods of testing for color-hlindness, and the study of color-sense. He has been over the whole subject before the recent observers I have mentioned, who have attached their names to this or that special modification. His method of examination with the worsteds:— to be given in his own words in this chapter — is therefore to be considered as a natural develop¬ ment of his special studies. March 31, 1871, he published his views on “ Color-Blindness and the Young-Helmholtz Theory of Color.”1 He there discussed this theory, and the methods heretofore used in testing color-blind¬ ness. He also gave the explanation of the peri¬ metric examinations afterwards carried out by him. By experiments with Maxwell’s rotating disk he found the true difference between red and green 1 Om Fiirgblindhet och den Young-Helmlioltz’ska Färgtheo- rien, 1871.