38 PROTOZOA AND DISEASE 



The act of sucking is described as follows by R. Newstead : l 

 ' The buccal organs are highly organized in all the members of 

 the ixodoidea, and are composed of four distinct bilateral parts. 

 When about to take food from its host, the animal fastens itself 

 firmly by its legs, depresses its rostrum, and implants the toothed 

 mandibles, and in proportion as these penetrate, the hypostome 

 follows, and the retrograde teeth on the under surface fix this 

 organ in the wound. In this way the hypostome and the mandibles 

 are driven into the wound to their full extent, and so firmly do they 

 become fixed in the derma that it is often impossible to remove 

 the tick without leaving the mouth organs attached to the host, or 

 tearing away a small portion of the skin.' 



The spiders and the ticks belong to the same class -theArachnida. 

 This class is subdivided into three orders : the Acarina (ticks and 

 mites), the Araneia (spiders proper), and the Scorpionida. Neumann' 2 

 mentions that there are 1,825 specimens of the tick family in the 

 British Museum. The acarina are the only parasitic order of the 

 class. 



Examples of the acarina that are familiar as human parasites 

 in this country are the Demodex folliculorum, very commonly found 

 in the plugs of secretion that fill the ducts of the sebaceous glands 

 of the face, constituting 'blackheads'; and the Acarus scabei, the 

 parasite that causes itch. Another arachnid, the minute harvest- 

 bug, Leptus autumnalis, 3 buries its long proboscis in the skin, and 

 causes an irritating eruption of red spots, erythema, or flat wheals, 

 and in some persons febrile disturbance. Moles, cattle, and horses, 

 as well as man, are attacked by it. In some countries e.g., the 

 Rocky Mountains and Africa certain kinds of ticks infest huts, 

 and, like the common bed-bug, attack the inhabitants only in the 

 dark. Severe illness, called tick-fever, may follow, but whether the 

 illness is in all cases caused by protozoal infection is not yet settled, 



1 R. Newstead, 'Pathogenic Ticks/ Brit. Med.Journ., December 30, 1905. 



2 L. G. Neumann, ' Notes sur les Ixodides,' Archives de Parasitologie, May, 

 1906. 



3 The Leptus autumnalis is probably the larval state of one of the Trombidiidce, 

 or running mites. 



