Quoted by L. Fleck, Genesis and Development of a Scientific Fact (Chicago and London: University of Chicago Press, 1979 [1935])
Description:

'The concept of infectious disease... is based on the notion of the organism as a closed unit and of the hostile causative agents invading it...

But not a single experimental proof exists that could force an unbiased observer to adopt such an idea. It is unfortunately beyond the scope of our discussion to examine all the phenomena of bacteriology and epidemiology one by one to show that the disease demon haunted the birth of modern concepts of infection and forced itself upon research workers irrespective of all rational considerations. It must suffice here to mention the objections to this idea.

An organism can no longer be construed as a self-contained, independent unit with fixed boundaries, as it was still considered according to the theory of materialism. [note: '"If the modern biologist wants to form an objective picture of the living world, he must rid himself of all ideas based on a subjective approach. It is sometimes not at all easy to get rid of such prejudices completely. Man's own consciousness as a self-contained whole or entity arouses in one the instinctive notion that the whole living world is divided into certain a number of units which we call organisms." Gradmann 1930, p. 641'] That concept became much more abstract and fictitious, and its particular meaning depended upon the purpose of the investigation. For the morphologist it has changed into the concept of genotype as the abstract and fictitious result of heredity factors. In physiology we find the concept of "harmonious life unit," according to Gradmann, "characterized by the notion that the activities of the parts are mutually complementary, mutually dependent upon each other, and form a viable whole through their cooperation." Morphological organisms of the type which are self-contained units do not have this ability. But a lichen, for instance, whose constituents are of completely different origins, one part an alga, another a fungus, constitutes such a harmonious life unit. The constitutents are closely interdependent and on their own are usually not viable. All symbioses, for instance, between nitrogen fixing bacteria and beans, between mycorrhiza and certain forest trees, between animals and photogenic [sic] bacteria, and between some wood beetles and fungi form "harmonious life units," as do animal communities such as the ant colony, and ecological units such as a forest. A whole scale of complexes exist which, depending on the purpose of the investigation, are regarded as biological individuals. For some investigations the cell is considered the individual, for others it is the syncytium, for still others a symbiosis, or, lastly, even an ecological complex. "It is therefore a prejudice to stress the idea of organism," in the old sense of the word, "as a special kind of life unit, a prejudice which is unbecoming to modern biology." [note: 'Ibid., [Gradmann, 1930] p. 666.] In the light of this concept, man appears as a complex to whose harmonious well-being many bacteria, for instance, are absolutely essential. Intestinal flora are needed for metabolism, and many kinds of bacteria living in mucous membranes are required for the normal functioning of these membranes. Some species exhibit for their vital functions an even greater dependence upon others. Their metabolism and propogation, indeed their entire life cycle, depend on a harmonious interference by other species. Some plants are pollinated by certain beetles; and malarial plasmodia depend for their life cycle upon their transmission by mosquito to man.

Now complex biological changes, within any complex biological individual, so construed are based upon phenomena which can be divided into several categories. They constitute either (1) a kind of spontaneous so-called constitutional process within the genotypes, such as mutations and spontaneous gene changes, roughly parallel with spontaneous radioactive phenomena within an atom. Many a disease belongs to this category, such as the hemolytic icterus of Nägeli, and even the outbreak of certain epidemics might perhaps be included here. Or they are (2) cyclic changes, of which some are genotypically conditioned and others are the result of reciprocal action within the complex life unit. These include the life cycle of organisms (aging), generational change, and some of the dissociation phenomena of bacteria. Both serogenesis and immunogenesis must be listed here, as well as virulence as a life phase of bacteria and even some infectious diseases, such as furuncolosis during puberty. Or lastly, there are (3) pure changes within the constellation of reciprocally acting parts of the unit comparable, for instance, to the reaction among ions in a solution. Hypertrophy of one element of the biological unit at the expense of another is a change of this type, as is the imbalance either consequent upon phenomena of the first or second category, or caused by external physio-chemical conditions. Most infectious diseases belong to this latter class. It is very doubtful whether an invasion in the old sense is possible, involving as it does an interference by completely foreign organisms in natural conditions. A completely foreign organims could find no receptors capable of reaction and thus could not generate a biological process. It is therefore better to speak of a complicated revolution within the complex life unit than of an invasion of it [note: 'Cf. Hirzfeld 1931, p. 2153.'].

This idea is not yet clear, for it belongs to future rather than present biology. It is found in present-day biology only by implication, and has yet to be sorted out in detail.

So construed, the concepts "sickness" and "health" also become unsuitable for any exact application. What used to be called infectious disease or the spread of epidemics belongs partly to the first, partly to the second or even third group of phenomena. Biologically, this also includes phenomena such as germ carrying, latent infection, the development of allergies, and even serogenesis. These have nothing directly in common with being ill, although they re very important to the mechanism of the disease. The old concept of disease thus become quite incommensurable with the new concepts and is not replaced by a completely adequate substitute.' (59-62)