The germ theories of infectious diseases / by John Drysdale.
- Drysdale, John James, 1817-1892.
- Date:
- 1878
Licence: Public Domain Mark
Credit: The germ theories of infectious diseases / by John Drysdale. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
63/78 page 59
![lowest order of individuality (§ 20), we have not to look for visible distinction of sexes. In independent individuals of this order, for the most part, either no sexual differentiation is found, or hotli sperm and germ-cells belong to the same individual. Nevertheless, we cannot say that any species can persist without sexual generation occurring in some part of the cycle of their life-history. According to Haclcel’s defini- tion, “ the criterium of sexual generation is the material union of two different generative substances,” and this is equally fulfilled by the process of conjugation proper to the lower orders of animate beings, whether the sexual elements are preceptibly differentiated or not. Asexual generation is represented in external nature by fission or fissiparous genera- tion and by spore-formation. Of the former there are two kinds, viz., simple division into two parts of equal age, and budding, in which a portion grows out, and is then detached, forming a product of different age. These processes are known to occur in partial bions, as we see in pus-corpuscles, which are the simplest type of disease-germs; hence, no doubt, Dr. Beale is so far justified in limiting his theory of disease-germs to those whose mode of propagation is proved, and to extend it further carries us into the region of hypo- thesis. Still, hardly any hypothesis could appear more marvellous and improbable—were we not familiar with them —than the phenomena of infection still unexplained by him. Asexual spore-formation has not been proved to occur with partial bions, otherwise that might account for some of the facts of long survival and dormancy of miasms. It is in the various forms of conjugation that we must hope to find analogies with the process of infection. In conjugation, a more or less complete blending of the protoplasm of two individuals, which apparently do not sexually differ, takes place. The result of this is the formation of what are usually called spores [zygospores], but which De Bary and](https://iiif.wellcomecollection.org/image/b22355248_0065.jp2/full/800%2C/0/default.jpg)
