APPENDIX 295 



parasites are really giant cells which have undergone 

 necrotic changes. 



Peculiar bright bodies which are visible in the masses of 

 molluscum contagiosiim, lying partly free and partly in the 

 interior of horny cells, are held by many to be coccidia, and 

 to be the exciting cause of the diseased growth. Others, 

 however, believe them to be merely degenerated epithelial 

 elements. 



Bodies of a similar nature have also been described (by 

 Darier, Wickham, and others) in the form of eczema of the 

 nipple known as Paget's disease, which is associated with 

 cancer of the mammary ducts, but Euffer and Walker ' are 

 of opinion that many at least of the appearances are 

 degenerating epithelial cells, or due to endogenous cell 

 formation. 



Wernicke has described coccidia in the granulomatous 

 tumours of mycosis fungoides. These are light yellow, 

 round, 3 to 30 /u. in diameter, and are contained in a 

 hyaline sheath. As many as ten have been observed in a 

 giant cell. They reproduce by segmentation, and the 

 young coccidia are set free by the bursting of the parent 

 cells. ^ 



C. The Action of Light upon Micro-organisms 



The action of white light. — The fact that certain effects 

 are produced upon micro-organisms by the sun's rays has 

 been known for some time ; thus certain pathogenic bacteria 

 show less marked activity after exposure to light, although 

 on the other hand some bacteria, probably only the aquatic 

 varieties (Buchner), grow better under these circumstances ; 

 and others belonging to the chromogenic species — Bacillus 

 prodigiosus, for example— cannot produce their pigment in 



■ Loc. cit. ' Centralb. f. BaU. u. Parasitenh., Dec. 28, 1892. 



