240 Progress of Rational Pathology. 



pendent on the place of growth of the parasite, and on the way 

 in which it is thrown off. The contagiousness is smaller, if 

 the parasite vegetates in the bowels, than if it be on the skin 

 or in the lungs. 3. Diseases are chronic, if the power of 

 propagation of the parasite is not limited ; acute, if after a 

 certain time it forms germs, and if the body in which these 

 germs are formed does not offer a bed adapted to their further 

 development. 4. Predisposition, is the capability of a body 

 to form a nursing bed for the parasites, without the capa- 

 bility of resisting their action. For every parasite does not 

 make the body on which it lives unhealthy : on the contrary, 

 nature is able to render this, as many other injurious in- 

 fluences, innocuous through habit, or to compensate for them 

 by nourishment. Contagions have, like all organisations, 

 specific preferences for particular soils and climates. Some 

 like a healthy body (most acute miasmatico-contagious 

 diseases :) others prefer a weakened and reduced one 

 (aphthae.) On the whole, the attraction and the develop- 

 ment of parasites appear to be favoured by a congested 

 state of the surface, on which they most usually spread, per- 

 haps on account of a partial separation of them from the 

 surface being caused by congestion, as the parasite of dysen- 

 tery and cholera by diarrhoea, of typhus by gastric fever, 

 of influenza by sneezing. As for entozoa, so for contagions, 

 there is a predisposition according to the age and kind of 

 animal : and in both the want of such predisposition may 

 be limited or unlimited. Contagion can become milder by 

 germinating in different families, or by repeated inoculation, 

 without losing the power of re-appearing again in full force 

 under favourable circumstances, (small-pox). The destruction 

 of the parasitic bed when the disease is over, reminds us of the 

 succession of different kinds of animals and vegetables in 

 infusions, in which each kind after a time exhausts the bed 

 fitted for its production, or rather for its nutrition. 5. The 

 miasmatico-contagious diseases are distinguished into local, 



