154 RHYTHM 



is coldest at the same time of the day, about 3.45 a.m., all 

 the year round. 



There is a curious relationship between the occurrence of 

 infantile diarrhoea and the temperature of the soil. This 

 very fatal disease is conveyed by flies which foul the food 

 of infants ; but it has been noticed that the disease does not 

 reach epidemic proportions unless and until the temperature 

 of the earth at a depth of 4 feet is about 56 degrees Fahren- 

 heit. In 1922 the temperature of the soil at this depth only 

 just reached this figure and there was no epidemic; but in 

 the late summer of the follo^ving year, 1923, the deeper 

 temperature stood at 58-9 degrees, and infantile mortality 

 due to diarrhoea rose to a figure higher than any recorded 

 since the autumn of 1921. 



Rhythm in Communities 



Merely because man happens to be a vertebrate, we are 

 rather apt to think that the Vertebrata are the most dominant 

 group of animals in the world. But in certain respects the 

 great group of insects can claim that position, at any rate as 

 regards land surfaces, for they are almost entirely absent from 

 the ocean. In number of species they surpass all other terres- 

 trial animals ; compared with the vertebrata their number is 

 colossal. It has been stated that the greater part of the proto- 

 plasm of the world is locked up in the bodies of insects. They 

 have further developed a social system, an art of living to- 

 gether in societies, more perfectly organized than those which 

 our civilization has succeeded in producing amongst men; 

 and they have actually achieved a high standard of industrial 

 and agricultural activity which facilitates their social life. 

 Familiar examples of these communities with individuals 

 specialized for the different kinds of work of the colony or 

 society needs are termites or white-ants, wasps and bees, and 

 perhaps the highest of all, ants. The first named, whose 

 white ant-hills sometimes attain a height of twenty feet, 

 are for the most part inhabitants of tropical or sub-tropical 

 countries, and the seasons have no effect upon their activities. 

 In thesame way the real ant communities carry on, but little af- 

 fected by changes of temperature, even in their most northerly 



