The poison, according to Kobert (1893), is a limpid, acid-reacting fluid, soluble in water but insoluble in absolute alcohol and ether. There are few data relative to its chemical nature. Wilson (1901) states that a common Egyptian species, _Buthus quinquestriatus_, has a specific gravity of 1.092, and contains 20.3% of solids and 8.4% ash. The venom of different species appears to differ not only quantitatively but qualitatively. The effects of the bite of the smaller species of the Southern United States may be painful but there is no satisfactory evidence that it is ever fatal. On the other hand, certain tropical species are exceedingly virulent and cases of death of man from the bite are common. In the case of _Buthus quinquestriatus_, Wilson (1904) found the symptoms in animals to be hypersecretion, salivation and lachrymation, especially marked, convulsions followed by prolonged muscular spasm; death from asphyxia. The temperature shows a slight, rarely considerable, rise. Rapid and considerable increase of blood-pressure (observed in dogs) is followed by a gradual fall with slowing of the heart-beat. The coagulability of the blood is not affected. An interesting phase of Wilson's work was the experiments on desert mammals. The condition under which these animals exist must frequently bring them in contact with scorpions, and he found that they possess a degree of immunity to the venom sufficient at least to protect them from the fatal effects of the sting. As far as concerns its effect on man, Wilson found that much depended upon the age. As high as 60 per cent of the cases of children under five, resulted fatally. Caroroz (1865), states that in a Mexican state of 15,000 inhabitants, the scorpions were so abundant and so much feared that the authorities offered a bounty for their destruction. A result was a large number of fatalities, over two hundred per year. Most of the victims were children who had attempted to collect the scorpions. The treatment usually employed in the case of bites by the more poisonous forms is similar to that for the bite of venomous snakes. First, a tight ligature is applied above the wound so as to stop the flow of blood and lymph from that region. The wound is then freely excised and treated with a strong solution of permanganate of potash, or with lead and opium lotion. In recent years there have been many attempts to prepare an antivenom, or antiserum comparable to what has been used so effectively in the case of snake bites. The most promising of these is that of Todd (1909), produced by the immunization of suitable animals. This antivenom proved capable of neutralizing the venom when mixed _in vitro_ and also acts both prophylactically and curatively in animals. Employed curatively in man, it appears to have a very marked effect on the intense pain following the sting, and the evidence so far indicates that its prompt use greatly reduces the chance of fatal results. THE SOLPUGIDA, OR SOLPUGIDS