DORMANT VITALITY, or 'rigor,' is a term used for an apparent suspension of vital activity, distinguished from death by the possibility of resuscitation. Two general classes may lie dis tinguished: (1) Dormant vitality induced by external conditions: and (2) dormant vitality determined by internal conditions. The first class is of three kinds: (a) Desiccation rigor. There are certain animals, notably rotifers, tar digrades, and nematodes, which can be dried in a vacuum until they become immobile, and can remain thus immobile for days or even months until, on the addition of water, they become active again. The organism has probably not lost all of its water, but has passed into an encysted condition; it is not dead, but its n•iab olism is greatly reduced. Even snails and other animals which can protect their internal tissues from complete loss of water may live for months without showing external activity. (b) Dark rigor is induced in green plants and even in certain fungi by their removal for several days from the light. The sensitive plant treated thus becomes immobile. Light is essential to move• ment. The reverse, or 'light rigor,' has been seen in bacteria. (c) t rigor.—The sensitive plant. muscle, and various other forms of protoplasm become quiescent at a temperature a few degrees below that at which they are killed by heat. The rigor seems to be due to the beginning of the death changes. Cold rigor occurs in simple protoplasm as it approaches the zero (centi grade) temperature. The chlorophyll granules of Vallisneria Iii ve only about one nun. per minute
at 1° C., and not at all at 0°: the rotation of Nitella ceases at 0° Cr.; in Tradescantia hairs, movement is wholly arrested on freezing the cell cap. Even in seeds and bacteria, which are not killed by the lowest temperatures, all vital activi ties have probably ceased at 0°. for De Candolle found that iu only one species out of ten could he get a seed kept at 0° to germinate. and even then germination was so retarded that it took from 11 to 17 days as opposed to 4 days at 5.7°. Likewise. bacteria do not multiply below 5° to 10°. Among animals Kulme found Amoeba cooled to near 0° almost motionless. Purkinje and Valentin first noticed that the ciliated epithe lium of the frog ceased its movements at 0°. Muscles of the frog were found by Kuhne to become at —3° to —7° a solid lump. which did not, however, wholly lack irritability. The evi dence of all these eases shows that activity nearly ceases in protoplasm at or near 0° C.
Determined by internal conditions, seeds, rest ing spores. cysts, gemmules of sponges, and stato blasts of Bryozoa are all conditions of natural dormant vitality. The period of dormancy is not unlimited. however, the alleged germination of seeds ninny hundred years old not being eon firmed. This indicates that even with a slow rate of living the food material eventually be comes exhausted.
Belief in human dormancy rests largely upon a certain collection of cases observed in India and published by James druid.