ARAN E A 



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T. ugubre Koch, Kara kist of Russia ; Segestria perfida St. ; Chceto- 

 pelina olivacea ; Lycosa tarantula L. ; L. singoriensis Laxman; 

 Epeira diadema Walck. 



Anatomical.— The body of the spider is sharply divided into 

 cephalothorax and abdomen. The pairs of appendages are six in 

 number: — (i) The two-jointed chelicerse; (2) the six-jointed leg- 

 like pedipalpi; (3-6) the seven-jointed legs. The poison gland 

 usually lies in the basal joint of the chelicera, ensheathed in con- 

 nective tissue, inside which there are two spirally arranged layers 

 of non-striped muscle surrounding a basement membrane which 

 bears two to three layers of polyhedral cells, surrounding the lumen 

 of the acinus. From the gland the duct runs forwards into the 

 distal hook-shaped joint, upon the apex of which it opens. 



The Venom, — -The venom, which is useful to the spider, enabling 

 it to kill the small animals upon which it lives, is an oily, trans- 

 lucent, lemon-yellow-coloured liquid, with an acid reaction and a 

 hot, bitter taste. It has proteid reactions, and gives the xantho- 

 proteic reaction. It is difficult to obtain it in any quantity. Wilson 

 recommends triturating the gland with distilled water (0-5 c.c. being 

 used for each gland), and then filtering, when an extract suitable for 

 experimental purposes is obtained. These extracts are rendered 

 harmless by heating to 90° C, and the active principles are said 

 not to dialyze. The chemical peculiarities and the active principles 

 of the venom are little known. Kobert, as has already been 

 pointed out, considers that there are two poisons: — (i) A toxin 

 secreted by the poison gland, and only causing local symptoms; 

 , (2) a toxalbumin distributed through the body (not originating 

 from the poison gland), and causing general symptoms. The first 

 exists alone in Lycosa tarantula, L. singoriensis. The second largely 

 predominates in Latrodedus . 



Kobert and Sachs have found and studied a hsemolysin, arachno- 

 lysin, in the venom of several kinds of spiders, and Sachs has been 

 able to immunize a guinea-pig against this toxin, and produce an 

 active serum. Arachnolysin acts upon the red cells of man, rabbit, 

 ox, mouse, and goose, but not on those of the horse, dog, sheep, 

 and guinea-pig. 



Spider-venom is also said to increase the coagulability of the 

 blood. The venom of Theridium lugubre is believed to act in- 

 juriously on the isolated frog's heart, even when diluted to i in 

 100,000, but it is not known whether this is due to action directly 

 upon the heart-muscle or upon the local nervous apparatus. The 

 walls of the capillaries are also said to be damaged by spider- 

 venom, and to allow an increased amount of transudation, and 

 hence the haemorrhages and oedema seen about the wound. It is 

 asserted that the venom acts deleteriously upon the mucous 

 membrane of the stomach and intestines, causing redness and 

 swelling, and even haemorrhages, which perhaps are due to some 

 attempt at excretion of the poison by these organs. It is also 

 thought that the venom acts upon the central nervous system, but 



