MICROBES AND PROTISTA. 7 
to rise, and from this point of view they are pro- 
fitable in industry and commerce. 
But in addition to these useful microbes, there are 
others which are injurious to us, while they fulfil 
the physiological destiny marked out for them by 
nature. Such are the microbes which produce dis- 
eases in wine; most of the changes in alimentary and 
industrial substances ; and, finally, a large number of 
the diseases to which men and domestic animals are 
subject. The germs of these diseases, which are only 
the spores or seeds of these microbes, float in the air 
we breathe and in the water we drink, and thus 
penetrate into the interior of our bodies, 
Hence we see the importance of becoming acquainted 
with these microbes. Their study concerns the agri- 
culturist, the manufacturer, the physician, the pro- 
fessor of hygiene, and, indeed, we may say that it 
concerns all, whatever our profession ‘or social position 
may be, since there is not a single day, nor a single 
instant, of our lives in which we cannot be said 
to come in contact with microbes. They are, in 
fact, the invisible agents of life and death, and this 
will appear more plainly from the special study we 
are about to make of the more important among 
them. 
Since it is easier to know and observe beings which 
are visible to the naked eye, we shall first speak of 
fungi—that is, of the larger microbes, with whose 
habits and organization we are also best acquainted. 
