MEDICINAL AND ECONOMIC PRODUCTS 321 



part in the evolution of modern medicine. Without skilled re- 

 searches on such animals it would never have been possible for 

 operative surgery to reach its present high pitch of perfection. 

 The prevention and cure of disease, other than by surgical 

 methods, have also benefited greatly in the past by such investi- 

 gations, and seem likely to benefit to a much larger extent in 

 the immediate future. 



Medicinal Value of Fish-Oil. It need only be said here that 

 the preparation of cod-liver oil, of which the Cod- Fish (Gadus 

 morrhud) is the recognized source, is a by no means unimportant 

 industry. 



Medical Uses of Insects. The Oil- Beetles (Meloidcz or Can- 

 tharidce) are so called 

 because they abound in 

 an irritant sort of oil, 

 which no doubt protects 

 them to some extent 

 from the attacks of insec- 

 tivorous animals. Some 

 of them are used to make 

 preparations for blister- 



7 . , . i r i F 'S- 1228. Spanish Fly or Blister Beetle (Lytta vesicatoria) 



ing- the skin, and of these 



a and b, Adults; c, larva. 



''blister-beetles the most 



notable are the "Spanish flies" (C ant har ides], belonging to South 

 and Central Europe. For commercial purposes a bright-green 

 species (Lytta vesicatoria, fig. 1228), collected in Hungary, is 

 most important. Various officinal extracts and plasters are pre- 

 pared from the dried bodies of these insects. 



Although Cochineal, another insect product (see p. 260), ap- 

 pears to have no value as a drug, it is largely used to give liquid 

 medicines an attractive appearance. 



Medicinal Use of Leeches (Discophord). Two kinds of Leech 

 are used for blood-letting, the commoner being the Medicinal 

 Leech (Hirudo medicinalis\ which is mostly collected in Spain, 

 France, and Italy. The Green Leech (H. officinalis] of Hungary 

 answers the same purpose. In these days the extent to which 

 these creatures are employed is comparatively small, but in the 

 Middle Ages, when blood-letting was esteemed a sovereign cure 

 for every ailment, the physician took his name from this favourite 

 remedy, and was familiarly known as a ''leech ". 



