68 
The N aturalist in La Plata, 
tliat in spring it was hard to find a survivor, even 
in the barns . and houses. The fact that species 
tend to increase in a geometrical ratio makes these 
great and sudden changes frequent in many regions 
of the earth ; but it is not often they present them- 
selves so vividly as in the foregoing instance, for 
here, scene after scene in one of Nature’s silent 
passionless tragedies opens before ns, countless 
myriads of highly organized beings rising into 
existence only to perish almost immediately, scarcely 
a hard-pressed remnant remaining after the great 
reaction to continue the species. 
