l886.] NEW-YORK MICROSCOPICAL SOCIETY. 119 



Bacteria occur everywhere. They are supposed to live and 

 grow in the water and in the soil, but their extreme minuteness 

 and lightness permit them under various conditions to be car- 

 ried into the atmosphere, so that, practically, they are every- 

 where. What sort of things are bacteria ? What do they look 

 like? These are difficult questions to answer. Observed singly 

 they are translucent. They are simply very minute cells whose 

 walls enclose a fluid substance. If magnified about ten million 

 times they would look like white grapes. They have neither 

 heads nor tails, and they are generally either round, rod-like or 

 corkscrew shaped Certain varieties are so minute that the 

 most powerful microscopes are required for their proper exam- 

 ination. Bacterium termo is only xsiTTTrth of an inch in length. 

 The means of locomotion possessed by some bacteria consist of 

 flagella. These appendages have not been discovered on all 

 kinds. The micrococci, as a rule, do not appear to move about. 

 Bacteria proper multiply by fission. The cell elongates, and 

 finally separates into two parts. Each of these parts subse- 

 quently elongates and divides in the same manner ; and so on 

 without limit. Fission takes place in some cases hourly. On 

 the first day or two the increase is comparatively slow, but after- 

 wards it becomes very rapid. A single Bacterium termo would, 

 in twenty-four hours, produce of its kind sufficient to occupy 

 the space of about rffV^jth of an inch. In five days enough 

 would be generated to fill the ocean, if the generations could 

 find enough food for their support. In the yeast plant, multi- 

 plication takes place as follows : The cell puts forth a little 

 bud which increases in size until it attains the dimensions of 

 the parent cell, and then drops off and itself -proceeds to de- 

 velop buds in a similar manner. Some bacteria have a very 

 curious way of continuing their existence under adverse cir- 

 cumstances — a very objectionable fact in the case of those 

 forms which are inimical to the health of man. Generally, the 

 bacteria perish when their food is exhausted ; but some of 

 them at such times curl up and remain quiescent until they are 

 supplied with additional food. Then they revive. This pro- 

 cess can be watched under the microscope. The bacterium, as 

 its food becomes scanty, shrivels up, and a little bright spot 

 shows itself. This is the spore. Around it the cell-wall of the 

 bacterium contracts and becomes exceedingly hard and firm. 



