1 68 SCIENCE FROM AN EASY CHAIR 



and of his body. Some of these cessations of activity 

 naturally and spontaneously occur in unsophisticated 

 mankind, when darkness falls on the earth at each suc- 

 ceeding evening. And it is hardly possible to doubt that 

 a tendency to periodic sleep has become fixed in the sub- 

 stance of living things by the alternation of night and day 

 as well as in some cases by the change of the seasons. 



I must conclude these notes about sleep by relating 

 a very curious case of sleep, resembling the winter-sleep 

 of higher animals, on the part of a snail. This was the 

 case of a desert snail from Egypt, which was withdrawn 

 into its shell, the mouth of the shell being closed with a 

 glistening film secreted by the snail, as is usual with 

 snails in this country in winter when they sleep. The 

 desert snail in question was affixed to a tablet of wood 

 in a glass case in the natural history department of the 

 British Museum on March 25, 1846. On March 7, 

 1850, that is four years afterwards, it was noticed by a 

 visitor looking at the case that the snail had emerged 

 from his shell and discoloured the paper around, but had 

 again retired. So the officials unlocked the case and 

 removed the snail from the tablet and placed him in 

 tepid water. He rapidly and completely recovered, 

 crawled about as a wide-awake snail should, and sat for 

 his portrait. This may be regarded as an instance of 

 unusually long sleep, natural to this species of snail, and 

 related probably to the frequently prolonged dryness of 

 the snail's surroundings. 



We are led by such a case as this on to what are 

 called examples of " suspended animation." Wheel- 

 animalcules, and some other minute creatures which are 

 found living in tiny pools of water, on the bark of trees, 

 and in the hollows of leaves, naturally dry up when the 

 water evaporates. You may dry them yourself in a 

 watchglass ; they appear as nothing more than shapeless 



