Some considerations on the phenomena of parasitism amongst protozoa / by E.A. Minchin.

  • Minchin, E. A. (Edward Alfred), 1866-1915.
Date:
[1910]
Catalogue details

Licence: Public Domain Mark

Credit: Some considerations on the phenomena of parasitism amongst protozoa / by E.A. Minchin. Source: Wellcome Collection.

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    difficult to detect.* These facts strongly suggest, as has been pointed out by medical authorities, that the parasites produce a specific toxin. Only in a single case, however, has it been claimed that a toxin has been isolated from a Protozoan parasite, namely the “sarcocystine” produced by the parasites of the genus Sarcocystis (Sarcosporidia).f The subject is one which remains to be investigated, and in the present state of knowledge it would be unprofitable to discuss it further here. The interaction of host and parasite is a question of great practical importance, which in consequence has been studied chiefly from the medical standpoint, that is to say, from the point of view of the host. I propose here, as I have already said, to deal with the question as a naturalist, and to discuss the problem rather from the point of view of the parasite ; and with this object I shall begin by a brief consideration of the facts of parasitism in general. A parasite is, like any other living being, an organism strug- gling for existence in a hard and cruel world. The difficulties, however, against which a parasite has to contend, in the struggle for existence, are different in many respects from those which beset a free-living organism. When once a parasite has obtained a footing in its proper host, the question of food-supply is solved for it, since it finds itself lodged in the midst of abundant nutri- tion so long as its host lives. On the other hand, if the species is to be maintained, it is essential that the offspring of the parasite should be able to infect new hosts—a matter usually of great difficulty, and one in which the chances are all against the parasite in most cases. To ensure dissemination of the species a large number of offspring must be produced, and special adaptations and mechanisms may be necessary. Hence in para- sites, the more they become specialised and adapted to parasitic life, the more the organs and functions of nutrition tend to become simplified, and the greater the tendency to elaboration of the reproductive system. It is especially amongst parasites * Compare Laveran and Mesnil, “Trypanosomes and Trypanosomiases,” translated by Nabarro (Bailliére, Tindal & Cox, 1907), pp. 146-150, t Comptes Rendus Soc, Biol. Paris LI. (1899), pp. 311-14.
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