734 DISEASES OF THE SKIN. 



Pathology. — " The nature of this disease is to be studied in tlie 

 botany of the cryptogamic parasite called the Tricophyton, dis- 

 covered by Malmsten in 1845. It consists of oval transparent 

 spores or globules, about ny-gVg- part of an inch in diameter. 

 Many of these are isolated, others constitute by their juxtaposition 

 articulated filaments. Its anatomical seat is the interior of the 

 roots of the hair. The hairs and fungi simultaneously increase ; 

 the former seem larger than usual, are paler in colour, lose 

 their elasticity, soften, and break off when they have risen some 

 one or two lines above the surface." — (Aitken.) 



Eing-worm may affect any part of the animal body, but its 

 favourite seats appear to be the hind quarters, back, neck, and 

 face. It is a contagious disease, and depends upon the presence 

 of the vegetable parasite already described. It differs fromfavus 

 in the colour of the scabs, which are greyish-wliite instead of 

 yellow. The microscopic appearance of the plant, its structure, 

 and its powers of propagation are identical with the Achorion 

 Schonleinii. " There are numerous facts which justify the belief 

 that there exists but one essential fungus, whose sporules find a 

 soil for development and growth upon the surface, or even within 

 more secluded portions of the body ; and that varieties in the 

 growth of that fungus are due to differences in the constitution 

 of the individual, to the moisture, exudation, soil, or temperature 

 under which the development of the fungus takes place. The 

 exact nature of these differences is not yet understood ; but the 

 production of irritant acids and gases are constant accompani- 

 ments of the growth of such parasites, by the chemical action of 

 the vegetable cell ; for it does not undergo development without 

 exciting a chemical decomposition in the pabulum on which it 

 feeds, and the different stages in its growth give rise to alcoholic 

 acid and putrefactive fermentations. Thus their irritant action 

 very soon may establish an eruption. But the ratio of eruption 

 to parasite is not constant ; for an amount of fungus which will 

 simply produce the death of hair in one person or part of the 

 body, may in another produce irritation, eruption, or violent 

 inflammation. These different results may be due to two causes 

 — (1), constitutional peculiarity in different individuals ; (2), 

 peculiarity of structure of a part as regards density, heat, mois- 

 ture, and chemical and anatomical composition of the part." — 

 (Aitken, Lowe.) 



Experiments are wanting to prove the possibility of the ring- 



