174 VEGETABLE PARASITES. 



discs are frequently pierced by a hair in the centre. There are 

 concentric furrows all around, dividing the scabs into a number 

 of rings, from J'" in breadth, gradually spreading on the outside. 

 The epidermis grows thicker on the edges, peels off, or remains 

 in the middle of the scabs. By onrefully piercing the epidermis 

 on one side, the scabs may be lifted off easily, and without 

 injury, from the cavity of the cutis, together with the adherent 

 neighbouring parts of the epidermis* The lower surface is con- 

 vex, yellow, smooth, and moist, from whence they can be stripped 

 off in the form of a rapidly drying layer of numerous, young, 

 round, and slightly granulated epidermal cells, which are rapidly 

 converted, on the edge of the scabs, into the great flat and irre- 

 gular epidermal cells of which the scab consists. Simon denies 

 the existence of a cellular layer between the cutis and scab. 

 Gudden always noticed such a layer breaking up into a mole- 

 cular mass in the neighbourhood of the fungus. The next 

 following layer of the favus becomes thinner towards the 

 centre, and ceases entirely in the middle of the cavity. It is of 

 a brimstone colour, ~ ^" in thickness all over the scab. 

 This is commonly called Gruby's capsule. It is best seen by 

 slightly pressing upon a thin vertical cut in the scab till the 

 layer separates from the inner darker mass, and by soaking ic 

 with water, when it may be unravelled by means of a needle 

 parallel with its perpendicular diameter, when the entangled 

 threads now and then exhibiting little vesicles of chlorophyll 

 are seen to advantage, and between them a molecular detritus. 

 The fungus spreads but little towards its lower end, whilst it 

 branches out variously towards its upper part, and makes rapid 

 transitions, at the inner border of the capsule, to the variously 

 intertwined rows of cells, which rarely exhibit a single thread. 

 These cellular rows and the detritus form the central, grayish- 

 white, and easily crumbled part of the scab, which are easily 

 crushed in water. A great number of little bubbles of air or 

 carbonic acid are seen at the place of transition to the filamentous 

 layer. The smallest scabs, which are scarcely seen with the 

 naked eye, form a flat crust, consisting only of filamentous favi, 

 and, imbedded in the upper layer of the epidermis, covered by 

 flat epidermal cells. It may be prepared by loosening the epi- 

 dermis, and is often quite inclosed by the latter; and the wind- 

 ings of the excretory duct of the perspiratory glands may even be 

 recognised at the lower part of this cellular layer, which, however, 



