GENEKAL CONSIDERATIONS. 117 



up, and to drive it asunder likewise in a downward direction in 

 order to prepare a bed for its roots; that the same display of 

 strength takes place on the human body, and thus enables the 

 spores, filaments, mycelia, &c., to penetrate its tissues. Mecha- 

 nical causes determine, therefore, the spores in penetrating 

 deeper into the under-lying tissue, and producing atrophy of the 

 fibres of the skin in these places. The cells containing the fat 

 disappear, as a section of the skin will show, and a cavity is 

 formed which is thinner at the spot where the growing parasite 

 has fixed itself. According to Robin, the eggs of the Helminthse 

 perforate the kernels of melons, apples, and cherries, and the in- 

 testines themselves, in accordance to the simple laws of mechanical 

 pressure. Inflammation of the tissue does not necessarily take place 

 in these places, although of little concern ; but a certain amount of 

 swelling, with or without the formation of pus-globules, may be 

 observed round the place of deposition (the cavity). A favus- 

 crust is formed, when the exuded mass coagulates and becomes 

 mixed with epithelium. This explains the migration of the 

 mycelia into the interior of the tissues and into closed cavities 

 just as easily as the migration of other foreign bodies from one 

 place of the body to another. The latter frequently takes, 

 instead of the molecule placed and resorbed before the foreign 

 body, another molecule on the opposite side, that is behind the 

 foreign body, and helps thus to push it forward. 



Prognosis. The preceding characteristics enable us, more- 

 over, to gain an insight into the kind of injury which the parasites 

 are able to do. They produce scarcely any critical symptoms, 

 at the utmost a slight disturbance of the bodily functions, whilst 

 they are restricted to a very small space, and live on animals of 

 considerable size. The quicker, however, they grow, the more 

 bulky they become ; the more important the organ is which they 

 choose, and the' more diminutive the body of the chosen host is, 

 the more obnoxious becomes their influence on the host, and his 

 very life may even be endangered by them. 



Absorption and penetration must not be confounded. The 

 vegetable parasite absorbs, by receiving liquid constituents into 

 its system without any change of the organic masses ; and it 

 penetrates, since it is a solid body which penetrates another 

 body, the tissues of which vanish beneath it by resorption ; and 

 this it does without changing its own condition. 



Parasitical plants as the causes of epidemic diseases. Without 



