TO PHYSIOLOGY AND PATHOLOGY. 27 



upon disease, and raising to a more scientific basis his knowledge of the remedial 

 agents to be employed ; then, indeed, it were of no avail to endeavor to support 

 this theory. Its simplicity has stood much in the way of its being generally 

 received ; for at the very time that every physician or physiologist does not hesi- 

 tate to ascribe the most striking changes in vital processes to bad nutriment, want 

 of fresh air, or the continuous use of salted food, &c. while no one feels any 

 scruple in assigning a scarcely appreciable difference of temperature as the cause 

 of inflammation, fever, and death one of the most important causes of a change 

 of form and properties is disregarded, as exercising no influence upon the organic 

 vital process. 



Here is a theory strengthened by a firmly linked chain of numerous and most 

 evident facts, to which a critical investigation is denied, although there is nothing: 

 that can be advanced against it save its comprehensibility. But it is precisely on 

 this latter character that the difference rests, which is observed in the result of 

 various methods of physical investigation. Although every pathologist and phy- 

 siologist is fully convinced that no organic process can be explained without the 

 co-operation of chemical and physical forces, every theory which has hitherto 

 been based upon such causes has been invariably doubted and rejected. 



If we compare the so-called chemical theory with the principles of the parasite 

 theory, we cannot comprehend how intellectual men, and the most practised 

 observers, can defend and lend their sanction to views which the experience of each 

 succeeding day must refute. 



THE PARASITE THEORY. 



The principles of the parasite theory may be referred to two facts, viz., to the 

 propagation of the itch, and to a disease appearing in silk worms called 

 muscardine. 



THE ITCH. 



The itch is an inflammation of the skin, occasioned by the irritation of a kind of 

 mite (acaru-s scabiei, sarcoptes humanus,*) which lives upon the skin, or, more 

 correctly speaking, burrows within it. For the communication of the itch con- 

 tinous vicinity is necessary, and that especially at night, as the itch mite is a 

 nocturnal depredator. The fact of the itch mite being the vehicle of the conta- 

 gious character of the itch, is proved by the following facts : inoculation with the 

 pus of itch pustule-s does not engender the itch, any more than the application of 

 the crusts of scabious pustules upon the arm. Secondly, the disease is healed by 

 rubbing off the mites with brick dust; and it can only be propagated by the 

 impregnated female animalcule. The itch may continue until it induces general 

 permanent disease, which in these cases becomes established, and cannot be 

 spontaneously cured. 



THE ITCH A CONTAGIOUS DISEASE PROPAGATED BY AN ANIMAL. 



Contagion of the itch is, according to this theory, an animal with a mandibular 

 apparatus, which lays eggs ; we term it fixed contagion, because it cannot fly, and 

 its eggs cannot be transported by atmospheric influence. 



If it be proved that the itch may be propagated by animals, it requires neither a 



* An excellent account of this insect, and of the other parasites infesting the human 

 body is given in VogePs Pathological Anatomy. See Dr. Day's translation, p. 419. 





