282 THE TREATMENT OF DISEASES. 



quently the twitching is perfectly obvious. As a rule, it affects one eye only. It 

 generally comes on as the result of worry or over-work, and is not uncommon in 

 business men. It is rather a feeling of discomfort than of actual pain. It may 

 result from over-indulgence in alcoholic liquids. The patient often wishes to get 

 rid of it, not because it gives him pain, but because people notice it, and think he is f 

 nervous or has been drinking. "We remember a traveller who was most anxious' 

 to be cured, because he had to go about soliciting orders, and found that no one 

 would deal with him ; " they suspected a man who could not keep his eyes straight 

 and look them in the face." Probably the best treatment is nux vomica (Pr. 44) or 

 pulsatilla (Pr. 43) ; should one fail, the other may be tried. Often enough, however, 

 it gets well " by itself, " as we say. The bowels should act freely, and the state of 

 the digestion should be inquired into. When there is debility, iron or quinine, or 

 both, may be given. 



Colour-blindness. This is a defect of sight by which the power of distinguishing 

 colours is either impaired or altogether lost. It is a subject of great interest, and 

 even of national importance. When we consider how many lives are daily dependent, 

 by land and sea, upon the accurate recognition by one person of the colour of a lamp, 

 how many accidents, otherwise inexplicable, have resulted from inability to dis- 

 tinguish colours, we are astonished that the subject has received so little consideration 

 in this country. Colour-blindness must have existed at all times, but the first case 

 of which we have any authentic record was published towards the end of the seven- 

 teenth century. A century or so later came the case of the great philosopher Dalton, 

 whose description of his own red-blindness is so well known as to have led many to 

 apply the term " Daltonism " to colour-blindness. There is a curious story related 

 of Dalton, which illustrates very aptly his want of appreciation of colour. He had 

 to be presented at Court, and being a member of the Society of Friends, some little 

 difficulty was experienced with regard to his dress. He declined to wear the sword, 

 which is an indispensable appendage of ordinary Court dress. The robe of a doctor 

 of civil laws was known to be objectionable on account of its colour one forbidden 

 to Quakers. Luckily it was recollected that Dalton was colour-blind, and that as 

 the cherries and the leaves of a cherry-tree were to him of the same colour, the 

 scarlet gown would present to him no extraordinary appearance. So perfect, indeed, 

 was the colour-blindness that this most modest and simple of men, after having re- 

 ceived the doctor's gown at Oxford, actually wore it for several days in happy un- 

 consciousness of the effect he produced in the street. 



As a rule, a colour-blind person sees red and sea-green as grey, scarlet and green 

 as yellow, and rose-colour and blue-green as blue ; whilst he can distinguish the 

 shades of red from each other, and also the shades of green from each other. If 

 such a person look at a red and a green through a red glass, the green will appear 

 darker, but the red will be nearly as bright as before ; through a green glass the red 

 will be darkened, but the green will be but little altered. In this way colour-blind 

 persons may distinguish the colours of a Turkey carpet. It is rare for a person to be 

 utterly destitute of all perception of colour, unless there be, in addition, some other 

 disease of the eye. 



The proportion of the colour-blind to the population generally is about four or 



