It was no wonder that he was clear and exact in his class lectures, for he based what he had to say on his own experiment and observation, and was at pains to verify experimentally the observations of others which came within his field.  Without verification he would not rely upon them.  Indeed, he was so careful to give nothing at second hand that one of his scientific friends gently reproached him for wasting his time in re-investigating matters already worked over by competent observers.  “Poor ——­,” he remarked afterwards, “if that is his own practice, his work will never live.”  Of his most important public addresses, two may be noted as especial tours de force.  On each occasion it was specially necessary to speak by the book, but at the last moment it was impossible to use the carefully prepared notes.  One was the address on the complex and difficult subject of “Animals as Automata,” at the Belfast meeting of the British Association in 1874, when the atmosphere was electrical after a Presidential address by John Tyndall which set theologians in an uproar.  Years afterwards he described the incident to Sir E. Ray Lankester:—­

    I knew that I was treading on very dangerous ground, so I
    wrote out uncommonly full and careful notes, and had them in
    my hand when I stepped on to the platform.

Then I suddenly became aware of the bigness of the audience, and the conviction came upon me that, if I looked at my notes, not one half would hear me.  It was a bad ten seconds, but I made my election and turned the notes face downwards on the desk.

    To this day I do not exactly know how the thing managed to
    roll itself out; but it did, as you say, for the best part of
    an hour and a-half.

    There’s a story pour vous encourager if you are ever in a
    like fix.

The other was his address at the opening of the John Hopkins University at Baltimore in 1876.  Late on the preceding afternoon he returned very tired from an expedition to Washington, to find that a formal dinner and reception awaited him in the evening.  He snatched an hour or two of rest, when a New York reporter arrived demanding the text of the address, which had to be sent to New York for simultaneous publication with the Baltimore papers.  Now the address was not written out; it was to be delivered from notes only.  From these notes, then, he delivered it in extenso to the reporter, who took it down in shorthand, and promised to let him have a copy to lecture from next morning.  But the fair copy did not come till the last moment.  To his horror he found this was written out upon “flimsy,” from which it would be impossible to read properly.  Again he turned it down on the desk and boldly trusted to memory.  This second version was taken down verbatim by the Baltimore reporters in their turn.  What if it did not tally with the New York version?  As a matter of fact, it was almost identical, save for a few curious discrepancies, apparent contradictions between professed eye-witnesses which the ingenious critic might perfectly well use to prove that both accounts were fictitious, and that the pretended original was never delivered under the conditions alleged.