THE UNDERLYING IDEA 67 
This naturally led the surplus sparrows out through 
the many thoroughfares leading from any large city. 
Where horses went sparrows could follow. Accord- 
ingly along the great lines of travel this bird found 
the simple path by which he could enter new territory. 
Meanwhile box-cars came into our large cities with 
freight. Sometimes they had carried grain, sometimes 
cattle. In either case it was not unlikely that a cer- 
tain amount of grain should be found scattered over 
the floor of such cars. The sparrow visited these cars 
for the grain, and it must have been no infrequent 
accident that a door should be shut upon a group of 
sparrows, especially in inclement weather, when they 
were apt to be huddled in a dark corner of the car. 
These prisoners would be carried to the destination 
of the car and there liberated, thus producing a new 
center of what we are now inclined to call infestation. 
By such means the English sparrow has spread over 
much the larger portion of the American continent. 
Few birds are bold enough to visit a railroad car. 
Of the few who might be tempted, most are timid 
enough to fly on the first approach of man. Hence 
they fail to gain this chance of spreading. They must 
remain in the old crowded home. Meanwhile the 
sparrow, thus transported, finds a new home with 
fewer or no sparrows. The struggle is less 
keen. More of his kind can live. His boldness 
