36 



THE POPULAR SCIENCE MONTHLY. 



nearly every tube that receives a centimetre of the water will become 

 turbid ; but, if the number of bacteria is only half as many, half the 

 tubes will remain sterile. This rule, though inexact in theory, seems 

 to prevail with an approach to exactness in practice. M. Miquel ap- 

 plied it to the estimation of the bacteria in rain-water, and found that 

 at the beginning of storms the water of precipitation contained a con- 

 siderable number, amounting sometimes to as many as fifteen per cubic 

 centimetre, and that the number immediately began to diminish ; 

 but that, strange to say, " after two or three days of moist and rainy 

 weather the meteoric water frequently contained more bacteria than 

 at the beginning of the rain. As the atmosphere was then in a condi- 

 tion of extreme purity a fact that was established simultaneously by 

 the statistics of the germs in the air it seemed to be shown that the 

 bacteria could live and multiply in the very midst of the clouds, or, 

 perhaps, that the clouds might in their course through space charge 

 themselves with a very valuable contingent of germs." 



In studying under the microscope the development of these little 

 organisms, in the preparations of which they have taken possession, a 

 very curious evolution of one of the microbes of the air is revealed. 

 The organism is a bacterium, which presents at first sight the charac- 

 teristics of a very long, filamentous bacillus. M. Miquel affirms that 

 he has seen this organism afterward divide itself into segments of 

 unequal size, in such a way as to form strings of micrococci. The 

 observation deserves consideration, for, if it is confirmed, and the 



Fig. 7. Successive Phases in the Transformation op the same Organism (after M. Miguel). 



Magnified 1,000 diameters. 



habit is proved to be general, it will establish a line of union between 

 the different types of the inferior algae, which were believed to be 

 fixed, but may be, after all, only transient genera. 



It is important to have the microbes collected in the broth of the 

 tubes sown in different kinds of liquors. Such treatment furnishes 



