4G2 DISEASES OF THE SKIN 



may not be restricted entirely to the affected region in which the parasites 

 are located, but may spread to other localities. This form, which is 



nothing more or less than eczema, pos- 

 sesses two peculiarities which may distin- 

 guish it at once from the common form 

 of eczema which is not produced by a 

 parasite : 



1. It invariably appears in single, 



isolated eruptive spots, and it is only 



after the disease has been present for 



some time, or where there is extensive 



Fig. 162.— Head of dog flea (Puiex irritation, that we may find the surface 



canis). (Megmn.) connected together. 



2. "We see the ajipearance of these eczematous eruptions in certain 



locations which are especially preferred by the parasites, and showing 



their greatest development of the eruption in those regions, even when 



the whole body is affected. 



A microscopical examination of the scales of the skin will furnish 

 definite information as to the character of the cause of the eruption. 

 We distinguish two groups of cutaneous parasites: First, those which 

 live upon the external surface of the skin, and, second, those which enter 

 the tissues of the membranes, penetrating deeply into the tissues. In 

 the first group we have the following: 



Ceratopsyllus Canis, Pulex Canis, the Dog Flea. 



The true dog flea, as well as the human flea (pulex irritans), is 

 found in the dog. The former is distinguished from the latter b}^ its 

 size, by the different length of its tentacles, and by the presence of a 

 number of sharp hairs arranged in a comb-like layer along the side of 

 the head (Fig. 1(32). Coarse breeds of dogs are not particularly affected 

 by the bites of fleas, but pet clogs and delicately bred animals scratch 

 and rub to such an extent as to cause irritated splotches and redness 

 over the entire body, and lead the owner to believe that the animal is 

 affected with mange. The skin is also filled with the small brownish- 

 black excrement of the flea. If the fleas are removed from the skin by a 

 bath or in some other manner, we may relieve the itching and irritation 

 by the application of some soothing solution. 



Therapeutic Treatment. — Fleas are best removed by means of 

 Persian insect powder (Flores pyrethri). This must be moistened with 

 alcohol and rubbed into the hair. The animal must stand on a sheet of 

 paper while this is being done, as the flea is not killed, but is only tem- 

 porarily stupefied by the action of the drug, and falls on the paper. The 



