RELATION TO OTHER SCIENCES 127 



logy has its closest relationship with the other sciences. Mechanics, 

 general and cosmic physics, geology not less than geography, in- 

 organic as well as organic chemistry, social and military history, 

 sociology, and commercial science, etc., must all be considered for 

 the enlightenment of the etiology of disease and the explanation 

 of the appearance of disease, especially in regard to time and place 

 (historic geographic pathology). But above all stand zoology and 

 botany, for the most important and most common diseases are 

 produced by living beings, by parasites. 



It is an old statement in pathology that a parasitic relation exists 

 in disease. For a long time the disease as such was thus per- 

 sonified; it was spoken of as an organism within the organism, a 

 parasite, which as Wunderlich * said, was anthroposed or phyto- 

 morphosed in every way. To it was ascribed an existence, a growth, 

 limbs and organs, a power of endeavor and of thought, even a sick- 

 ness, death, and finally a corpse. Pathology has done away with 

 this conception. It is true that we still speak of the disease, of 

 cholera, typhoid fever, pneumonia, etc., and that in practical medi- 

 cine we still speak of treating this or that disease. A treatment for 

 syphilis, for diphtheria, or some other disease is recommended as 

 if we spoke of something tangible, independent. But all this is only 

 for convenience of expression, and we know very well that what we 

 call a disease is not an entity but only a group of phenomena which 

 have for their basis a common cause. There are really no diseases, 

 but merely sick men, diseased organs, diseased tissues, diseased 

 cells, and it is the cause of these disturbances which brings about 

 the special phenomena which we observe in the diseased part. 



This cause may be a parasite. Centuries ago the opinion was occa- 

 sionally expressed that diseases were caused by living beings, which 

 disturbed the life-processes in the human body. In the middle of 

 the last century the view that there must be contagium vivum 

 was victoriously upheld by Henle, 2 but only in the last decades 

 of the nineteenth century was actual proof brought fonvard that 

 by far the commonest causes of disease are living organisms which 

 live parasitically on or in the human body. The disease is not the 

 parasite, but one parasite or many parasites cause those variations 

 from the normal structure and function of parts of the body which 

 in their entirety we call disease. 



By parasitology a close union is made between pathology and 

 the described natural sciences and thus with general biology. 



The great biologic question as to the origin of the lowest being 

 is related principally to the human parasites. In spite of the state- 

 ment of the great English physician Harvey, "Omne vivum ex ovo," 



1 Wunderlich, Hdb. d. Patholog. u. Therap. i, p. 12, 1852. 



2 Henle, Hdb. d. Ration. Pathol. n, 2 p. 457, Braunschweig, 1853. 



