on Muscular Motion . 
5 
and while my mind was strongly impressed by them, a favour- 
able opportunity occurred. Ayoung man came into St.George's 
hospital with a cataract in the right eye : this proved to be a 
fair case for an operation, to which the man very cheerfully 
submitted, and was put under my care for that purpose. 
In performing the operation, the crystalline lens was very 
readily extracted, and the union of the wound in the cornea 
took place unattended by inflammation, so that the eye suf- 
fered the smallest degree of injury that can attend so severe an 
operation ; these circumstances it is proper to mention, as 
they contributed to render the patient a more favourable sub- 
ject for experiment. 
The man's name was Benjamin Clerk ; he was a seafaring 
man, 21 years of age, and in perfect health. Both his eyes were 
free from complaint till about the 11th of April, 1753, at which 
time he was on a voyage home from the East Indies, a sud- 
den mist or dimness appeared before his right eye ; this in- 
creased very rapidly, and on the 18th of the same month the 
sight was entirely obscured. The crystalline humour was ex- 
tracted on the 25th of November; and 27 days after the ope- 
ration the eye was so far recovered as to admit of the fol- 
lowing observations and experiments being made upon it. 
In this man we had all the circumstances combined, which 
seemed to be required to determine how far the crystalline lens 
was the principal agent in adjusting the eye. The man himself 
was in health, young, intelligent, and his left eye perfect ; the 
other had been an uncommonly short time in a diseased state, 
and appeared to be free from every other defect but the loss of 
the crystalline lens. He very willingly allowed me to make 
the following experiments on him; and remained in town. 
