Of course, the post-mortem appearances of poisoning, except in a few instances, are not very characteristic. As every medical man is aware, poison, if administered with a criminal intent, is generally in such a dose as to take immediate effect--although this is by no means necessary, as there are numerous substances which accumulate in the system, and when given in small and repeated quantities ultimately prove fatal--notably, antimony. The diagnosis of the effects of irritant poisons is not so difficult as it is in the case of narcotics or other neurotics, where the symptoms are very similar to those produced by apoplexy, epilepsy, tetanus, convulsions, or other forms of disease of the brain. Besides, one of the most difficult facts we have to contend with in such cases is that poison may be found in the body, and yet a question may arise as to its having been the cause of death. CHAPTER XXVIII. "POOR MRS. COURTENAY." Ambler appeared to be much concerned regarding the poor man's death. When we had first met beside his vegetable barrow in the London Road he certainly seemed a hard-working, respectable fellow, with a voice rendered hoarse and rough by constantly shouting his wares. But by the whispered words that had passed I knew that Ambler was in his confidence. The nature of this I had several times tried to fathom. His unexpected death appeared to have upset all Ambler's plans. He grunted and took a tour round the poorly-furnished chamber. "Look here!" he said, halting in front of me. "There's been foul play here. We must lose no time in calling the police--not that they are likely to discover the truth." "Why do you say that?" "Because the poor fellow has been the victim of a secret assassin." "Then you suspect a motive?" "I believe that there is a motive why his lips should be closed--a strange and remote one." Then, turning to the old fellow who had been the dead man's friend, he asked: "Do you know anyone by the name of Slade?" "Slade?" repeated the croaking old fellow. "Slade? No, sir. I don't recollect anyone of that name. Is it a man or a woman?" "Either." "No, sir." "Do you know if Lanky Lane ever had visitors here--I mean visitors not of his own class?" "I never 'eard of none. Lanky wasn't the sort o' chap to trouble about callers. He used to spend 'is nights in the Three Nuns wiv us; but he'd sit 'ours over two o' gin. 'E saved 'is money, 'e did." "But look here," exclaimed Ambler, seriously. "Are you quite certain that you've never seen him with any stranger at nights?" "Never to my knowledge." "Well," my companion said, "you'd better go and call the police." When the old fellow had shuffled away down the rickety stairs, Ambler, turning to me, said abruptly: "That fellow is lying; he knows something about this affair."