188 



PREVENTION AND TREATMENT OF SCABIES. 



then require to be mixed with a proper active principle. 

 Soaps are used in dipping, but they are only fit to clean the 

 wool, and are washed out readily. They are valuable in skin 

 diseases, but, like the oils, require to be mixed with proper 

 materials so as to destroy the vermin. 



Itch and mange are known to be essentially skin diseases, 

 curable alone by topical remedies; and the medicines used 

 are valuable almost in proportion to the rapidity with which 

 they destroy the life of the parasites which give rise to the 

 irritation and other morbid appearances. About fifty years 

 ago, Walz sought to prove the efficiency of agents by observ- 

 ing their effects on acari placed under the microscope. This 

 method has since been adopted by Gerlach, Hertwig, and 

 others; and the subjoined table embodies the facts ascer- 

 tained with reference to the time in which different sub- 

 stances will destroy acari : 



