VITA LATENTE. – Latent life falls within the field of biological adaptations. It is to be understood as a reduction to the minimum of every vital activity, but one cannot speak of an interruption of it: interruption of life is death, and what is dead does not revive. Latent life occurs when environmental conditions become so unfavorable as not to permit full vital activity.
The term latent life has been employed by biologists for conditions that are also very different, both physiological conditions that normally occur in the life cycle of organisms, such as the condition of seeds, spores, cysts, diapause, and winter or summer dormancy (hibernation and aestivation), and accidental conditions, as in many cases of encystment and hypnosis, as well as pathological conditions, such as forms of thanatosis or catalepsy. When latent life reaches its minimal expression, it is designated as “anabiosis”; for many authors, the term latent life should be limited to this aspect alone, considering dormancy on the one hand and hypnosis on the other as very different conditions, although they have certain points in common.
The important feature of all these aspects of latent life is the possibility of returning, through appropriate processes, to active life. The first observation of the ability of animals in “apparent death” to “return to life” was made by Antonio Leeuwenhoek in 1701, in rotifers. Only forty years later was an analogous observation made on rotifers and grain eels by Baker and Needham, who succeeded in reviving these animals merely by wetting the dried material. The sensation caused by this report was so great that these authors, under the weight of the harshest criticism, had to retract what they had observed. In 1776 Lazzaro Spallanzani, although he himself had initially attacked the conclusions of these authors, announced, after conducting numerous experiments, the truth of these facts. But the controversy did not cease; indeed, two currents of thought emerged: one of the “resurrectionists,” headed by Doyere, and one of the “antiresurrectionists,” headed by Pouchet. The former even admitted a “momentary death” caused by desiccation. The controversy became so heated that a commission was formed, in which men such as Berthelot, Broca, and Brown Sequard took part. Its verdict (1860) was acceptance of the resurrectionist point of view, based on the fact that without water one cannot speak of life. Today, however, no one accepts this conclusion, since desiccation is never complete and a minimum of life remains in the organism; “reviviscence” is nothing other than a reintensification of quiescent vital processes. The correct term “minimal life” is due to Spallanzani, while that of latent life, introduced by Claude Bernard in 1879, also aptly indicates this concept.
Nevertheless, even after the authoritative affirmations concerning the concept of minimal life, some authors, such as Kochs (1890), returned to the concept of a true arrest of life; the term “anabiosis,” introduced by Preyer (1891), denotes this “suspension” of life. But these resurgences of “resurrectionist” thinking no longer find credence today. Let us examine some particular conditions of latent life, such as those of seeds and spores. Exaggerated claims have been made in this regard—for example, concerning the possibility of germination of wheat found in the tombs of the Pharaohs; but Acton demonstrated that after thirty years wheat is no longer capable of germinating. The result obtained with the Pharaohs’ wheat was due to the naivety of the experimenters, who had fallen victim to crude frauds. Nevertheless, seeds display astonishing resistance to unfavorable environmental conditions: De Candolle and Fictet obtained the sprouting of seeds brought to –200° C. It should be noted that respiration is already no longer appreciable at –10°. It has been established that refrigeration acts in the same way as desiccation. Becquerel (1904–1910) attributed great importance in these phenomena to the protective barriers that form and prevent the passage of air and carbon dioxide. This author obtained normal germination of fungal spores even after a stay of twenty-five months in a vacuum and of twenty-four days at a temperature between –180° and –253° C. It has been demonstrated that the various enzymatic systems persist in quiescent seeds.
Another form of latent life is that determined by low temperature, even in higher organisms, and which may generally be defined as “stiffening.” In a higher animal placed in the cold, respiration slows, internal body temperature decreases, and cardiac contractions become less frequent. These phenomena cause the animal to fall into a profound torpor and then into sleep; in animals for which this condition is normal during the winter months, it is called “hibernation”; it is called “stiffening” in those forms that do not normally possess the capacity for hibernation. In these animals, if the fall in temperature has been too great, the process is irreversible. Cold-blooded vertebrates (fish and amphibians) can nevertheless be frozen and subsequently made to resume their activity. Hibernation is a biological problem of great interest. The decrease in temperature is the stimulus that causes it, but the animal is already predisposed to this condition by its intimate anatomical and physiological constitution. An animal that enters hibernation passes through several stages: first light sleep, then medium and finally deep sleep, and thereafter once again light sleep. Physiological activities gradually decline through a mechanism similar to that of anabiosis. Heartbeats decrease, as does respiration.
(photograph: Bildarchiv d. Ö. Nationalbibliothek)