20 



KNOWLEDGE 



[Januaby 1, 1895. 



The ivy is a very convenient plant for microscopical 

 study. With a wet razor one can easily make transverse 

 and longitudinal sections which show admirably the 

 principal features in the histology of dicotyledons. The 

 cross section of the stem forms a beautiful microscopic 

 object. Fig. II. shows a ring of twenty fibro-vascular 

 bundles, in the centre of which are seen the large thin- 

 walled cells of the pith. The space between the vascular 

 ring and the epidermis is filled with cortical parenchyma, 

 also consisting of thin-walled cells. Connecting this latter 

 with the pith are plates of cellular tissue, which pass 

 between the bundles and are called the medullary rays. 

 In Fig. III. a single bundle is shown more highly magnified. 

 In this we may note on the left the air canal ; next 

 this a quantity of bast composed of thick-walled or 

 Eclerenchymatous cells ; inside of this is the soft bast, the 

 inner portion of which is the cambium layer, where the 

 cells are seen undergoing division. The wood of the 

 bundle lies just inside the cambium ; its cells are repre- 

 sented in a darker shade. Large spiral vessels are seen 

 towards the inner part of the wood, and on the face 

 of the bundle next the pith are more thick-walled 

 sclerenchymatous cells. One of the stellate hairs is 

 represented on the outside. Bundles similar to the above 

 compose the veins of the leaf ; while a section of the leaf 

 shows that in the ivy the difl'erence between the upper 

 stratum of closely packed palisade cells and the lower 

 one of laser tissue is especially marked. The palisade 

 cells, covered by the upper epidermis which is devoid 

 of openings, constitute a tissue adapted to retain water, 

 and the tissue of the lower half of the leaf is full of 

 large intercellular passages ; the cells, in fact, only form 

 a kind of framework. These passages communicate 

 with the external air through the stomata on the under 

 side of the leaf. This lower stratum is, therefore, a 

 tissue which has been specialized for the elimination 

 of watery vapour. The epidermal cells of the leaf, as in 

 a number of cases, present a wavy outline — bordered 

 pits, not unlike those of the pine, occur in the cells of 

 the wood ; but a better idea of the anatomical structure 

 will be obtained from the drawings than from any descrip- 

 tion in words. 



Geographically the ivy is an outlier, being the only 

 European representative of its family ; the rest of the order 

 are tropical or sub-tropical, a significant circumstance, 

 going to show that the ivy has acquired its peculiar 

 characteristics in adaptation to the more rigorous con- 

 ditions of colder latitudes. 



THE SCORPION'S STING. 



By C. A. Mitchell, B.A.Oxon. 



AMONG invertebrate animals the scorpion occupies 

 an invidious position very similar to that held 

 by the serpent among the vertebrate. Each is 

 regarded with fear and dislike, and to each a 

 malignity has been attributed which it does not 

 possess. The scorpion, perhaps, has suti'ered even more 

 than the serpent from this exaggerated disgust ; but 

 although its fierceness may justify some of the epithets 

 applied to it, it is but fair to take into account the fact 

 that it only uses its weapon for the natural purposes of 

 procuring food and defending itself when molested. 



There are upwards of two hundred species of the scorpion 

 known, but only about a dozen are found in Europe. The 

 larger and more dangerous species all occur in tropical 

 countries, and in India arid Africa are sometimes fatal to 

 human life. The three kinds which have been most 

 studied are Srorpiu curnpaus, which is common in caves 



in South Europe ; Scoi-pio oiritanus, also a European 

 species ; and Scurpin afcr, the dreaded African scorpion. 



The poison apparatus is situated in the last of the six 

 joints of the tail. It consists of a bent, horny sting, having 

 on each side of it a long opening communicating with the ■ 

 two glands secreting the poison. When running, the 

 scorpion has its tail curved over its back, and on striking 

 suddenly straightens it, thus bringing the sting downwards. 

 At the moment when it is preparing to strike, a droplet of 

 poison has been seen to exude from the duct, but more 

 is forced out when the sting meets the resisting body. 

 The amount of poison secreted, at any rate in the 

 European varieties, is very small. .lusset estimated the 

 quantity in a specimen of H. occUanux, two inches in length, 

 at '03 of a grain. This quantity, however, was sufficient 

 to kill a fair-sized dog, and Paul Bert found that a scorpion 

 of about the same size contained enough to rapidly destroy 

 three frogs in succession. 



From the difficulty of obtaining sufficient for the purpose, 

 the chemical nature of the poison has been but little 

 studied. In appearance it is a clear, limpid liquid, with a 

 pungent smell and slightly acid reaction. It is soluble in 

 water in all proportions, but is insoluble in alcohol and 

 ether. Its density is a little greater than that of water. 

 Under the microscope transparent epithelial fragments and 

 fine granular matter may occasionally be noticed. The 

 fact that it is coagulated by alcohol points to its being of 

 an albuminoid ' nature, and this would agree with Joyeux- 

 Laftuie's suggestion that it is of analogous composition to 

 snake venom, possibly containing some principle similar to 

 the I'chidnin obtained by Prince Lucien Bonaparte from 

 the venom of the viper. The fine granules referred to 

 above are soluble in acetic acid and weak solutions of 

 potash, but beyond this little is known of their properties 

 or of what ]part they play in the action of the poison on 

 the animal system. 



The physiological etJ'ects of the venom as a whole have 

 been frequently described since Maupertuis proved, in 1731, 

 that though the sting of the common scorpion might prove 

 fatal to a small quadruped, such a result was very rare. 

 The general symptoms following a sting are (1) local 

 inflammation, [2) convulsions caused by the action of the 

 poison on the nerve centres, and (3) paralysis from its 

 action on the extremities of the motor nerves. 



Jusset stated, as the result of his experiments, that the 

 venom acted directly on the red corpuscles of the blood, 

 causing them to adhere together, thus obstructing the 

 entrance to the capillaries, and stopping the circulation. 



Other observers, however, do not confirm his conclusions. 

 According to Paul Bert the blood is not affected. He found 

 there was no alteration in the blood of the heart of 

 frogs which had died from the effects of the sting, with 

 the exception of one case where it appeared very dark at 

 first but reddened on contact with the air. In no instance 

 was its power of coagulating destroyed. He, therefore, 

 considered the venom as a nerve poison only, which, like 

 the South American poison nii-arc, acted on the motor 

 nerves while it left the sensibility untouched, but which, 

 unlike curaiv, produced violent convulsions analogous to 

 those produced by strychnine. Valentin+ suggested the 

 possibility of using rurair as an antidote. When a little of 

 this substance was introduced under the skin of frogs before 

 being stung, the symptoms were greatly modified and 

 electrical stimulus now produced no muscular contraction. 

 The frogs recovered in two or three days, while others not 

 thus treated perished from the effects of the sting. 



As in the case of the bite of a venomous serpent, the 



See Knowlbbse, June, 1894. t Zeit.fiir Biolor/ie, Bd. XII. 



