132 PHOTO-MICROGRAPHS. 
end of three hours, in twenty-four hours the num- 
ber will amount to more than sixteen millions and 
a half At the end of two days this bacterium 
will have multiplied to the incredible number of 
281,500,000,000; at the end of three days it will 
have furnished forty-seven trillions ; at the end of 
a week, a number which can only be represented 
by fifty-one figures.” 
The smallest micrococci are less than one-fifty- 
thousandth (0.54) of an inch in diameter. The 
periods upon this page measure about one-fiftieth 
of an inch in diameter. A sphere of the size of 
one of these periods magnified one thousand times 
would be equal to a spherical mass twenty inches 
in diameter, — the ball of a twenty-inch cannon, 
for example ; but the micrococcus magnified one 
thousand diameters would only equal the small 
sphere represented by the period. Comparing 
the mass, we find that it is as 1 to 785,400,000. 
It is not surprising that these minute plants for 
a long time eluded the observation of micro- 
scopists, and that it is only during the last few 
years that they have received the study which 
they deserve. For aside from their interest to 
biologists as the lowest of living organisms, they 
have an interest for physicians and sanitarians as 
the probable cause of certain infectious and epi- 
demic diseases. This is not, however, the place 
to discuss this question, which is still under inves- 
tigation. 
The aureole of transparent substance around the 
micrococci in Fig. 2 seems to be peculiar to this 
