( HAP. IX. I 1 HI'- BALANCE OF I 73 



bacilli of plague and cholera, which also take their toll of human 

 life. 



\.s noted above, the three destructive factors which are probably 

 most important in maintaining the balance of life arc climate. 

 tood. and enemies. In a country such as India we Scarcely need 

 to be reminded of the great importance of climatic influences. 

 Print in the monsoon rainfall means loss of crops whilst undue 

 excess may cause disastrous Hoods. So far as man himself is con- 

 cerned loss of crops may mean famine, although here the human 

 intellect comes to his assistance' by providing irrigation schemes to 

 render him less dependent on the monsoon rainfall and rapid 

 means of communication (railways, mad: ) bj which supplies may 

 be brought in from other more favoured districts. Hut for ol 

 animals the effects of climate in lessening the food-supply may be 

 very serious. 



The subject ol enemies is so vast that it can only be stated here 

 that it is the exception for any animal or plant to die of pure old 

 age. At every stage of its existence it is subject to attack, within 

 and without, by parasites which live at its expense and by preda- 

 ceous animals or plants which kill it outright. In the fictitious 

 insect whose rate of increase was considered at the commencement of 

 this chapter, for every egg successfullj deposited it was seen that 

 ninety-nine failed to reach a state of reproductive maturity, and 

 such a stringent rate of selection is the rule in the case of insects 

 under natural conditions of existence. 



