PAEASITES OP ANIMALS. 39 



gen, is disagreeable, and it should be used, therefore, where 

 there is plenty of ventilation. This is an exceedingly valua- 

 ble remedy, also, for the itch of man, as well as the " mange" 

 of animals. The sulphuret of potassium comes in the form 

 of grayish or greenish lumps, put up in tight bottles. It is 

 used in photography and can usually be bought at the princi- 

 pal drug stores. 



An equally useful preparation, having the same properties, 

 may be easily made by taking fresh quick-lime, slacking it 

 gradually with water, and forming a milky solution by the 

 addition of more water, as in the preparation of white-wash. 

 Into this put as much flowers of sulphur as will dissolve by 

 boiling for some time. This will produce a deep yellow solu- 

 tion like that of the sulphuret of potassium in odor and 

 effects. It may be diluted if too strong. It contains sul- 

 phuret of calcium^ upon which its usefulness depends. Sul- 

 phur may also be boiled in potash lye, to produce a similar 

 preparation, and to this, wliile boiling, tobacco is sometimes 

 added, but the sulphur is, no doubt, sufficient for all practical 

 purposes. But in no case can we be certain of destroying all 

 the eggs of these parasites by any wash whatever, that would 

 not be dangerous to the animal. Therefore the treatment 

 should be repeated two or three times, at intervals of ten or 

 twelve days, in order to destroy any young that may have 

 hatched in the meantime. 



The Head-louse of man QPediculus capitis DeGeer). Pig. 30. 



This is, probably, the best known species of the genus 



Pediculus. It is still sufficiently common among persons who 



Fiffure 30. neglect personal cleanliness, though much less 



so than it is said to have been formerly, when it 



was thought no disgrace in some parts of the 



old world, but was regarded as fashionable, 



rather than otherwise. This insect is almost 



exclusively confined to the human head. It 



attaches its eggs firmly to the hair, near the 



roots. These eggs are long-oval, with several 



little conical prominences at the large end, 



rigure 30. — Head-louse {Pediculus capitis DeGeer), greatly magnified.. 

 From Packard's Guide. ' 



