176 PRACTICAL PAKASITOLOG-Y 



dehydrated with alcohol in stages of gradually increasing strength. 

 Otherwise, water will be retained in the tissues, and the objects, when 

 mounted, will be more or less opaque and, in this condition, useless. 

 Oil of cedar-wood is frequently used as a clearing reagent, but in this 

 case also the specimens must be very carefully dehydrated, as the 

 oil absorbs water very readily. 



(1) ACARINA (MlTES). 



Of the Acarina which are known to be parasitic in man, two only, 

 Sarcoptes and Demodex, are of permanent parasitic habit. All other 

 varieties are occasional in their occurrence. They may be either the 

 permanent or the occasional parasites of animals, adopting man as an 

 accidental host; or they may be free forms, living in and on organic 

 substances and attacking man only under certain favourable condi- 

 tions. The greater number of species, including Sarcoptes and 

 Demodex, are so extremely small that their examination is a matter 

 of some difficulty to the beginner. For this reason it is advisable to 

 begin with the group Ixodidae, certain members of which attain a 

 comparatively large size. Two species of Ixodidse are readily 

 obtainable in almost all parts of Central Europe ; they are Ixodes 

 ricinus (L.) and I. hexagonus, Leach, commonly known as wood-lice, 

 or dog-ticks. They live in the leafy undergrowth of woods and 

 plantations where, in order to obtain nourishment, they seek to attach 

 themselves to one of the higher vertebrates. Thus, their most 

 frequent hosts are wild animals (game), grazing cattle, dogs, and 

 man. 1 



Specimens of Ixodides do not by any means all look alike. The 

 empty tick changes considerably in appearance when the intestine 

 becomes filled with blood and is in process of digestion. Moreover, 

 there is considerable difference between the larva, the nymph, and 



4 In addition to the above-named, the following varieties are met with in 

 Germany : Ixodes tenuirostris, G. Neum., on Arvicola varieties in England and the 

 Isle of Riigen ; Hcemophysalis punctata, Can. et Fanz., on grazing cattle and game 

 animals, in districts bordering the Mediterranean, in Holland and in the neighbour- 

 hood of Nuremberg ; H. concinna, Koch, on grazing cattle and game, in France, 

 Austria and Brunswick; Dermacentor reticulatus (Fabr.), on grazing cattle and 

 game, in South and West Europe, in Asia, in North and Central America and in 

 Wurtemberg ; and Argas reflexus (Fabr.), the European hedge-tick or pigeon-tick, 

 found in pigeon-cots and on pigeons, rare in Germany. Tho other varieties which 

 are said to occur in Germany are probably developmental stages of either Ixodes 

 ricinus or I. hexagonus. The Ixodidae have attracted considerable attention 

 within the last few years ; since, in fact, it has been recognized that, like Anopheles, 

 Culex and Glossina, they are the carriers of infectious diseases (Texas fever of 

 cattle). 



