396 DISEASES OF THE SKIN. 



CUTANEOUS AFFECTIONS WHICH ARE CAUSED 

 BY ANIMAL PARASITES. 



The changes produced on the skin from disease caused by animal 

 parasites are divided into two conditions — primary and secondary. 



The primary appears as a superficial inflammatory process, pro- 

 duced directly by irritations of the parasites upon the skin, and 

 this condition depends to a large extent upon the amount of irri- 

 tation and the depth that the parasites have penetrated in the skin. 



The secondary symptoms are the results of this penetration into 

 the cutis, causing more or less itching and irritation, and, as a rule, 

 scratching and rubbing on the part of the animal, producing heat, 

 redness, papules, vesicles, pustules, hemorrhages, or excoriations. 

 These irritated spots 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, 

 possesses two peculiarities which may distinguish 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 irritation, that we may find the surface connected 

 together; and, 



2. We see the appearance of these eczematous eruptions in cer- 

 tain 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 erup- 

 tion. 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, puncturing deeply 

 into the tissues. In the first group we have the following: 



Ceratopsyllus (Pulex) Canis, the Dog- Plea. 



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

 found in the dog. The former is distinguished from the latter by 

 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 



