1895.] NATURAL SCIENCES OF PHILADELPHIA. 255 



much greater but for human aid. On the other hand it must he 

 said that these animals have been removed from their native habitat, 

 and that their special exposure to danger is a result of Mans inter- 

 ference with nature's adaptations. 



Organic competition takes various forms. An indirect struggle 

 between species is constantly going on. The food supply is in every 

 case limited, and is the object of an increasing contest between the 

 individuals of a species and separate species, in which the most 

 vigorous individuals or the best adapted species are likely to win. 

 In this contest size and strength of a species are rarely assurance of 

 success. Size may be detrimental, as necessitating more food, while 

 strength is of little avail where the contest ants are not directly 

 pitted against each other. The mastodon, for example, needing 

 great quantities of herbage for its food supply, might, in cases of 

 severe drought, succumb to the food competition of the rabbit, or 

 some still more insignificant creature, which, spreading in vast 

 numbers over the country, devoured the sparse herbage and left its 

 huge competitor to starve. An army of locusts has more than once 

 ! nought great numbers of men to the verge of starvation, despite 

 Man's intelligent and combined resistance. The potato bug is 

 capable of depriving a nation of its food, and a blighting fungus may 

 destroy the crop upon which a whole people relies. It needs all 

 Man's care and prevision to prevent insect foes from destroying his 

 food supply. The lower mammalia have no modes of defence 

 against such assaults and no power of providing granaries of food 

 against times of need. Thus hosts of herbivora may have frequently 

 perished in consequence of an insect assault upon their food; and 

 numerous carnivora, thus deprived of their food, may have similarly 

 perished. Yet on the other hand, the lower plant-eating mammalia 

 an' much less exposed than Man to this special danger, from the 

 fact that few of them feed, like him, on fruits and seeds, their 

 general food supply being the abundant grasses, and the leaves and 

 twigs of trees, a supply which is much less likely to fail. 



An adverse influence, of the nature of direct assault, and one 

 which at times may have been enormously destructive, remains to 

 be mentioned. Tins is the aggressive action of the minute organisms 

 known as bacteria, of which the disease- producing species have at 

 times proved the most dangerous of all the known enemies of Man. 

 At present, however, the indications are that they are much less 



