This labor consisted principally in the collection of evidence with regard to the traffic, and the presentation of it before the public mind. In this labor Clarkson was particularly engaged. The subject was hemmed in with the same difficulties that now beset the Anti-slavery cause in America. Those who knew most about it, were precisely those whose interest it was to prevent inquiry. An immense moneyed interest was arrayed against investigation, and was determined to suppress the agitation of the subject. Owing to this powerful pressure, many who were in possession of facts which would bear upon this subject, refused to communicate them; and often after a long and wearisome journey in search of an individual who could throw light upon the subject, Clarkson had the mortification to find his lips sealed by interest or timidity. As usual, the cause of oppression was defended by the most impudent lying; the slave-trade was asserted to be the latest revised edition of philanthropy. It was said that the poor African, the slave of miserable oppression in his own country, was wafted by it to an asylum in a Christian land; that the middle passage was to the poor negro a perfect elysium, infinitely happier than anything he had ever known in his own country. All this was said while manacles, and hand-cuffs, and thumb-screws, and instruments to force open the mouth, were a regular part of the stock for a slave ship, and were hanging in the shop windows of Liverpool for sale. For Clarkson's attention was first called to these things by observing them in the shop window, and on inquiring the use of one of them, the man informed him that many times negroes were sulky and tried to starve themselves to death, and this instrument was used to force open their jaws. Of Clarkson's labor in this investigation some idea may be gathered from his own words, when stating that for a season he was compelled to retire from the cause, he thus speaks. "As far as I myself was concerned, all exertion was then over. The nervous system was almost shattered to pieces. Both my memory and my hearing failed me. Sudden dizzinesses seized my head. A confused singing in the ear followed me wherever I went. On going to bed the very stairs seemed to dance up and down under me, so that, misplacing my foot, I sometimes fell. Talking, too, if it continued but half an hour, exhausted me so that profuse perspirations followed, and the same effect was produced even by an active exertion of the mind for the like time.