ACHORION SCHCENLEINI 



691 



FIG. 328. Vertical section through an hair 

 with a portion of a favus cup. 



potash must never be washed in water because contact with water would reduce 

 them to powder at once. 



In favus-infected hairs treated with potash numerous mycelial threads 

 will be seen, and in addition very short, occasionally rounded, bodies pseudo- 

 spores, or mycelial spores which are 

 resistant forms, and not true spores or 

 conidia which are only produced in cul- 

 tures. 



The mycelial filaments which are 

 arranged along the axis of the hair are 

 delicate knotted and simple, or provided ^ 

 with two to four branches. The pseudo- 

 spores are 3-T/* in diameter, rounded or 

 slightly flattened ; they do not infiltrate 

 the whole of the hair but form branched 

 chains separated from one another. 



The parasite passes through the epithelium 

 to reach the dermis : it destroys the hair 

 papilla and causes the hair to fall out. In 

 the neighbourhood of the favus cup there is 

 an hypertrophy of the epithelial cells and, in 

 the midst of these, masses of mycelium 

 agglutinated together with an amorphous 

 glairy substance. To study the parasite in 

 the scutulum, crush up one of the scabs 

 between two slides and treat the powder 

 with caustic potash as described above. A 

 scutulum may be embedded in paraffin, cut and stained in gentian- violet or Unna's 

 polychrome blue. 



The parasite has the following characteristics in the hair : 



(a) There is no visible envelope. As a matter of fact an envelope exists 

 but it is very refractile and difficult to make out. 



(b) The mycelium has a knotted appearance and the filaments composing 

 it are wavy. 



(c) The parasite never affects the whole of the hair. 



(rf) The filaments divide into three or four branches resembling the bones 

 of the human tarsus (tarsefavique). 



2. Cultural characteristics. Conditions of growth. Achorion schoenleini is 

 distinguished from the moulds and resembles the tricophyta in that it does 

 not grow on acid media (Duclaux and Verujski) ; a degree of acidity exceeding 

 O3 gram of tartaric acid per litre is sufficient to completely arrest growth. 

 To obtain a culture of the parasite a medium rich in peptone must be used ; 

 most carbohydrates are unsuitable : glycerin (broth or agar) and mannite are 

 the best. The parasite is aerobic. Growth begins at 15 C., the optimum 

 temperature is 33 C. ; at 38 C. growth ceases. 



The appearances presented by Achorion schoenleini in culture are not at 

 all characteristic : they vary even when the same strain is grown on the 

 same medium. 



Achorion schoenleini is not present in pure culture in the lesions of favus 

 and in order to isolate it in pure culture Krai's method should be adopted. 

 Grind up a little piece of the scutulum in a sterile ground-glass mortar with a 

 little sterile powdered silicic acid. Plate the powder on gelatin in Petri 

 dishes, examine the plate before incubating and mark the spots where single 

 spores have been sown, then incubate the plate and subsequently pick off the 

 colonies which develop in the situations marked. 



