DEVELOPMENT OF THE GERM THEORY. 21 



identical, he states that we have not the smallest reason, from 

 knowledge or analogy, to assume that any gaseous, mineral, or 

 vegetable matter diffused from the atmosphere or exhaling from 

 the earth, could create a disorder or spread it in a manner so 

 remarkable over the globe ; and equally inapplicable, for the same 

 reasons, is every theory founded on the temperature, habits, food, 

 or other conditions of particular communities. 



Further, he says, it must be kept in mind that we have to deal 

 here with immigrating malaria, a wandering cause of disease, 

 capable not merely of being diffused through the atmo- 

 sphere and conveyed along vast tracts or lines over the globe, 

 affecting diiferent places with a varying intensity which no known 

 condition of earth, atmosphere, or human habits can explain, 

 but also possessing the power of reproducing itself so as to 

 spread the disorder by fresh creation of the virus which first 

 evolved it. This faculty of reproduction stands foremost among 

 the conditions essential to a right theory of cholera; all our 

 reasoning stops short unless under recognition of the fact so 

 stated. Without it there would seem a physical impossibility in 

 explaining the phenomena of the disease, and particularly its dis- 

 tribution and succession in different places and seasons. A 

 thorough study of these singular details of its history, keeping 

 this principle constantly in view, will not only confirm and illus- 

 irate the latter, but will lead us to organic life as the only conceiv. 

 able source and subject of such reproduction. It is against all the 

 analogy of nature to suppose this power to belong to inorganic 

 matter. Either animal or vegetable life, in their simpler forms, 

 must furnish the material cause we seek for, since to them alone 

 can belong the faculty of renewing indefinitely the active cause of 

 the disease. 



These enlightened views were held by Sir Henry Holland, and 

 give the fullest early account of the germ theory of disease which 

 I am able to bring before you. They form a brilliant example of 

 the scientific use of the imagination, and although again very 

 forcibly brought forward by Henle in 1840, it was a theory hardly 

 accepted by the profession, and very many years elapsed before 

 any proofs were forthcoming in support of it. 



Indeed, if we pass over a period of thirty-six yeaes and take 



