Etiology. Pathogenesis. 847 



rays of the sun (E. solare), especially if the skin has previously 

 been damp. In these cases the ultraviolet rays of the sunlight 

 cause the inflannnation. 



Different chemical substances that cause loosening of the 

 epidermal layer or irritate the skin may cause eczema, even if 

 only used once. This may occur, especially after the applica- 

 tion of gray mercury ointment (Eczema mercuriale), mustard 

 oil, cantharides, croton oil, tartar emetic, iodine, balsams, pe- 

 troleum, carbolic acid, tar, etc. ; the affection also arises after 

 the prolonged internal use of these drugs, and this is especially 

 so in the case of mercurial eczema. 



Of internal causes, diseases of the digestive organs are first 

 to be considered (E. symptomaticum). Catarrhal diseases of 

 the stomach and intestine especially, exert such an influence, 

 for abnormal products of fermentation which are absorbed, 

 probably affect the blood vessels of the skin or reduce its power 

 of resistance to external injuries (autointoxication). 



Weakening and exhausting diseases (fluke, verminous 

 bronchitis, rickets, diabetes, etc.) cause a predisposition to 

 eczematous affections. Other diseases of the skin, especially 

 scab, also produce a decided predisposition to eczematous in- 

 flammation, but especially to moist eczema in the dog. Very 

 fine skinned as well as old and fat animals, especially dogs, 

 show a marked tendency to this disease, and individual and 

 racial differences are evidently of importance in this respect 

 (among dogs the pug dog, the poodle, the bull dog and the 

 Leonberger [this is a breed of dog originally bred by Herr 

 Burger of Leonberg, Wiirttemberg. Trans.] are subject to the 

 disease). 



Schindelka repeatedly saw an eczematous skin disease, and finally nephritis, 

 developing in consequence of constipation in the dog. He considers it probable that 

 the toxins absorbed frona the intestine irritate the skin on the one hand and the 

 kidneys on the other. 



The mode of origin and the course of eczema render it very probable that 

 microorganisms, especially schizomycetes, are of importance. Hardly any experi- 

 ments have been made in animals in this direction, and up to now those under- 

 taken in humans have produced no conclusive result. Unna, who like Niemeyer, 

 considers eczema to be a catarrh of the skin, found a species of cocci in the vesicles, 

 scales and sections of skin, and also observed the development of eczematous patches 

 after experimental inoculations with these cocci. Ravolgi found staphylococcus 

 pyogenes albus, Bernheini the same coccus, and likewise the staph, citreus as well 

 as the diplococcus albicans tardus ; Scholtz found the st. citreus, Veiel found pyogenic 

 staphylococci. According to the last named author the bacteria pass through the 

 spaces between the epidermal cells into the skin and into the lymph spaces, and 

 in this way cause the inflammatory process. Probably different kinds of bacteria 

 exert a similar effect on the skin or on the tissue of the cutis. In one case of tail 

 eczema in the horse, Casper proved the streptococcus pyogenes to be the cause of 

 the disease ; Baer on the contrary in eczema rubrum of a dog, found a micrococcus 

 as the causal factor. 



Pathogenesis. Eczema is essentially an inflammation of 

 the superficial layers of the skin, in the course of which the blood 

 vessels of the papillary bodies dilate and the non-pigmented 



