224 



KNOWLEDGE. 



[UCTOBEE 1, 1694. 



But our present concern is chief!)' with the secretions 

 produced hy these insects. The oil beetle receives its 

 popular name from the fact that, when handled, it causes 

 a deep yellow, oily liquid to exude from between the 

 segments of its body, and from the joints of the limbs, 

 a proceeding which makes it a decidedly unpleasant insect 

 to have much to do with. Oil beetles may be found in 

 early spring, crawling slowly about among the grass of 

 meadows, and beside footpaths. They may easily be 

 recognized by their dull bluish-black colour, rough, uneven 

 surface, and enormously large abdomen, which is only very 

 partially covered at its base by the shrivelled and crumpled 

 elytra, or so-called wing-covers, though there are no wings 

 to cover. This ponderous body (speaking of the female 

 insect) trails along the ground as the creature goes on its 

 toilsome way, seeking a suitable place for laying its eggs. 

 The yellow exudation is of an acrid character, and has the 

 power of raising blisters, if applied to the skin in sufficient 

 quantity. For this reason, oil beetles have been used in 

 medicine, especially for veterinary purposes, the chief 

 supply having been obtained from certain districts in south- 

 west Eussia. A German writer states that a century ago 

 the oil of these beetles was used in central Europe as a 

 remedy for hydrophobia, and in Sweden it is said to have 

 been employed for the alleviation of rheumatic pains. 



While one species of oil beetle [Mehiii iiruscdralxnis) is a 

 common insect with us, and may freijuently be seen in 

 grassy places in early spring, its more important relative, 

 the true Spanish tly, or blister beetle of commerce (Fig. 

 17), is very seldom met with in this country, though there 

 have been occasions, notably in the year 

 1837, when it has appeared in profusion 

 in certain localities. Scientifically it is 

 known, as we have already said, either 

 as Lijtta vesicatorid or Cuntharis vcsicutoria, 

 the specific name having reference to its 

 blister - producing properties. It is a 

 beautiful insect, of a shining green colour, 

 and with a large square head. ISy its 

 colour, as well as by the facts that 

 its body is comparatively narrow and 

 parallel-sided, and that the wing-covers 

 lie side by side and are long enough 

 to cover the body, it may be easily 

 distinguished from the oil beetles with their bluish-black, 

 stout, oval bodies, and short elytra, which slope sideways 

 away from each other, and so reveal the abdomen between 

 them. It is abundant in many places on the Continent, 

 and the market was first supplied from Spain, whence it 

 became generally known as Spanish fly. 



I'nlike the oil beetles, the blister beetles are arboreal in 

 habits, frequenting a variety of trees, such as ash, privet, 

 lilac, olive, &c. They appear about midsummer, and 

 during the hottest parts of the day they descend from the 

 trees, and that of course is the best time for securing 

 them. Their presence is pretty easy to detect, for, apart 

 from their brilliant colour, they emit a powerful scent. 

 Indeed it is said that the characteristic substance to which 

 they owe their valuable property is so volatile as to affect 

 the air immediately around the trees, and thus make it an 

 act of imprudence to sleep under those in which they are 

 abundant. The active principle is called cantharidin, and 

 many experiments have been made with a view to dis- 

 covering in what part or parts of the insect it is produced, 

 as well as whether or not its production is confined to the 

 adult stage. In the year 1813 it was chemically examined 

 by the French sai-ont Robiquet, who obtained it from the 

 beetles in the form of a white substance in flat crystals, 

 which were found to be insoluble in water, but soluble in 



I'iii.i; 



^J'iVU- 



isli Kly, or Blister 

 Beedo. 



alcohol, ether, and other liquids. A chemical formula, . 

 C-HgOn, has since been assigned to it. It has powerful 

 vesicating properties, for the huudi-edth part of a grain, 

 when enclosed in thin paper and applied to the lips, caused 

 pain to be felt in about a quarter of an hour, and soon 

 after little blisters appeared. When a salve was ajiplied 

 to these, the heat caused it to melt and run, with the result 

 of carrying the vesicant with it, and thus multiplying the 

 number of pustules, thereby increasing instead of allaying 

 the discomfort. 



The experiments of Beauregard were specially directed 

 towards localizing the substance in the body of the insect, 

 and they were carried out by making small plasters of 

 different parts of the beetles and applying them to his 

 own body. His main conclusions were that cantharidin 

 occurred most abundantly in the blood and in certain 

 parts of the reproductive organs in both sexes. Whenever 

 any of the softer parts of the body, still wet and charged 

 with blood, were applied to the skin, they soon produced 

 blisters. Even the elytra, when separated from the living 

 insect, and therefore still containing a small quantity of 

 moisture within their tissues, were found to be capable of 

 causing a similar result. They were applied to the arm 

 by their inner surface, in which the skin would be thinner, 

 and therefore the blood would be more easily able to afiect 

 the operator. The dry membrane which thus intervened 

 between the vesicant and the skin of the arm of course 

 retarded the process, but still, after the lapse of seven 

 hours, a good blister was produced. When, however, the 

 elytra were cut up in shreds, and dried with blotting 

 paper, so that all moisture was removed from them, only 

 a very shght eflect was produced even by a prolonged 

 application. Thus it was evident that the active principle 

 was to be looked for in the juices of the wing rather than 

 in its solid substance. 



The strongly vesicating power of certain parts of the 

 reproductive apparatus of course suggested that the 

 function of cantharidin in the economy of the insect 

 might be connected in some way with the reproductive 

 process. But that such is not necessarily the case evi- 

 dently follows from the fact that the insect possesses the 

 property to a greater or less degree in all its stages, 

 including those in which it is sexually immature. Even 

 the eggs are possessed of the blistering power, though 

 this perhaps is no more than might be expected, since the 

 ovaries are strongly impregnated with cantharidin. In 

 1883, Beauregard took a portion of a freshly laid batch of 

 eggs, and working them up into a paste with a little water, 

 applied the little plaster so formed to his arm. After 

 four hours, the smarting produced was sufficiently intense 

 to lead him to stop the experiment. He therefore removed 

 the plaster, and a few minutes after an enormous blister 

 appeared on the spot, attesting the strongly vesicating 

 property of the freshly laid eggs. In the larv;c the 

 property was found to be much less intense. Ten larva;, 

 several days old, were crushed and made into a plaster, 

 which was applied as before. Even after eight hours 

 nothing more than a considerable inflammation was 

 developed, and no blister appeared. When, however, a 

 larger application of the crushed bodies of two dozen 

 similar larvic was made, a blister was produced after the 

 lapse of the same time. 



To collect the insects for medicinal purposes, a plan is 

 adopted which closely resembles that known to ento- 

 mologists as " beating." A large cloth is spread on the 

 ground beneath the branches of the trees on which the 

 insects are to be found, and then the branches are 

 vigorously shaken, so that the beetles fall on to the cloth. 

 Being but sluggish in their movements, they have little 



