OKIGIX OF DISEASK AND THE GERM THEORY. 155 



being the time for action, the febrile temperature is therefore 

 more easily borne at that time than it is during the night. 



The division of time into months has reference to the phases 

 of the moon. It has been suggested by Darwin that men- 

 struation points to an ancestral time when spring-tides brought 

 an extra supply of food. The fact that delivery occurs usually 

 at the time of a menstrual epoch, and the times at which ante- 

 partum haemorrhage occurs, may likewise be thus referred to 

 bygone external agencies. 



Next we come to the rhythm presented by the different sea- 

 sons. Now it is clear that summer and winter differ, in some 

 degree, as day and night do ; and they likewise merge into each 

 other imperceptibly. In summer there are more light, more 

 heat, and more food, and also greater activity of the vital pro- 

 cesses. In spring and summer, as compared with winter, the 

 pulse of an animal is quicker, the temperature higher, and, in 

 short, metabolism is more active. With each recurrence of 

 spring, life, comparatively dormant during the winter, bursts 

 into renewed activity, and the hibernating animal comes out of 

 its quarters, revives, and takes on renewed activity. Reproduc- 

 tion of ail kinds of animals takes place at this season of the 

 year. There is also a great increase in peripheral growth, for 

 instance, of hair, nail, and hoof, and the old hair and cuticle 

 are shed. 



We concluded, above, that increased vital activity had been 

 for such a long time associated with day as to explain the fact 

 that organisms exhibit a rhythm corresponding to the alterna- 

 tion of day and night. Now there is also some evidence to show 

 that organisms exhibit another rhythm corresponding with the 

 alternation of summer and winter. According to the Rev. J. G. 

 Wood, some Australian plants, set in the suburbs of London, 

 made an attempt to blossom just as our winter set in ; but in 

 the course of a few years they were gradually later in blossom- 

 ing, until they had found the proper season, and thenceforward 

 they put forth their leaves and flowers at the same time as our 

 indigenous plants. 



When animals are first introduced into a fresh environment, 

 they sooner or later enter into competition with one another. 

 At any time many of them may be called upon to fight, or to 

 make good their escape. In either case, the associates of work 



