Progress of Rational Pathology. 239 



animal origin.) We may consider as endowed with relatively 

 independent life, the elemental forms of organisations, which 

 inherit the power of nourishing and of propagating themselves, 

 only as parts of an organic whole, though they do not in- 

 stantly die on separation from that whole. Many reasons make 

 us suspect, that the contagious organisations belong to the 

 lower kinds of plants and animals, (in short, have an absolutely 

 dependent life of their own). Thus the origin of epidemic 

 diseases can often be traced to circumstances, which favour the 

 development of the lower animal and vegetable organisations ; 

 for instance, the destruction of organic substances, in over- 

 filled or ill aired spaces. The means, which favour, impede, 

 or destroy the action of the infectious matter, are the same 

 which are favourable and destructive to the life and reproduc- 

 tion of the known lower organisations. Of late years an infinite 

 number of such low parasites has been discovered, occurring 

 in plants as well as in animals and men ; and on comparing 

 the action of contagions and miasmas with the consequences 

 of the formation of parasites in the lower animals, we are 

 struck by many analogies : from this comparison the following 

 results may be deduced : — 1. Purely contagious diseases are 

 caused by parasites whose germs do not maintain themselves in 

 the air, or in a dry condition (itch) ; those parasites may be 

 considered as a middle grade, which cannot maintain them- 

 selves for a long time dry : in short, those diseases which are 

 infectious, through the medium of air it is true, but only in the 

 immediate neighbourhood of the patient, (glanders, consump- 

 tion). To produce epidemics, a contagion must be motionary : 

 but every motionary contagion does not necessarily produce 

 epidemics, only one, for which the constitution has a general 

 predisposition (for instance the contagion of Tinea.) 2. 

 Miasmatico-contagious disease occurs in individual cases and 

 epidemics, purely from miasma : in such cases the parasite 

 lives and grows, but does not form any fruitful germs within 

 the diseased body. The degree of contagiousness is also de- 



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