170 VEGETABLE PAEASITES. 



During the first period the hair becomes altered, not so the 

 skin at the place of its germination ; gastric disorders are seldom 

 or never found. 



During the second period the change in the hair becomes 

 more perceptible ; the fungus appears outwardly as a yellowish 

 concretion, with or without being preceded by congestion of the 

 skin, and exhibits all its regular stages of development. 



During the third period the alteration of the hair has reached 

 a high degree, the hair falls off by itself, and leaves merely scars 

 behind. The few diseased places are covered with lichenous 

 debris, or crusts resembling pulverized alum or gypsum. 



The species of the favus are nothing more than variations in 

 form according to the different states of reaction of the cutis in 

 relation to the fungus. Thus the following forms may be traced: 



1 . Favus disseminatus, F. isolalus, F. independens, F. urceolaris y 

 Porrigo favosa, Tinea lupinosa, F. alveolaris, &c. It is found on all 

 parts of the body covered with hair, but more especially on the back 

 of the head, spreading sometimes over the whole surface of the 

 body (Favus generalis], now alone, now associated with other skin 

 diseases, and particularly with Herpes circinnatus. It has likewise 

 three periods. During the first, which is of various duration, 

 there exists sometimes a disordered digestion, sometimes riot. 

 The hairs are frequently altered, without lustre, feeble, and 

 strikingly differing from the colour of the healthy hair; finally 

 they become quite colourless. On endeavouring to pull out the 

 hair it offers little resistance, and the microscope shows its texture 

 to be very much altered. The parts which constitute the shaft 

 are wholly or partially destroyed. The colour is a dirty, grayish 

 or brownish-like rust or blight. Distinct traces of the fungus 

 are observed at the bulb and at the continuation of the root of 

 the hair. 



Gastric disorders become frequent during the second period. 

 If the fungus is examined at its origin with the naked eye, it 

 appears mostly as a yellow, scarcely perceptible point, with a 

 ventral impression, pierced by a hair. The first trace of the 

 development of the fungus may be discovered by means of a 

 pocket-lens ; sometimes a slight rising of the skin is observed on 

 the spot where the hair penetrates it, sometimes a small point 

 aside and underneath the skin, or also two or three small, yellow, 

 isolated concretions parting at the basis of the hair, which form 

 on the following day a single, conically excavated concretion 



