50 A 1IALF-HOUK WITH THE 



plant appears as a red stain upon the surface of 

 damp objects. If a little of this red matter is 

 scraped off the object to which it is attached, and 

 placed under the Microscope, it will be found to 

 consist of a number of separate minute cells, as 

 represented at figure 89, plate 4. This plant 

 belongs to the same family as the red-snow plant, 

 and there are a number of forms of these minute 

 organisms, which, on account of their rapid growth 

 and red colour, have given rise to alarming appre- 

 hensions, in former times, when their true nature 

 was imperfectly understood. One of them attacks 

 bread, and gives to it the appearance of having 

 been dipped in blood. They also attack potatoes. 

 Of the same simple structure, but not having a red 

 colour, is the yeast-plant, or fungus, shown at 

 figure 90, plate 4. This plant abounds in yeast, 

 and may also be found in porter and ale. If 

 vinegar is allowed to stand for some time, a 

 minute plant is developed, called the vinegar- 

 plant. In its earlier stages of growth it exhibits 

 elongated cells, looking like broken pieces of 

 thread, seen at figure 91. Threads more fully 

 developed are often seen in decomposing fluids, 

 and upon the surface of decomposing animal and 

 vegetable substances ; such is the so-called cholera- 

 fungus, which may be obtained by exposing damp 

 slides to the air. They are shown at figure 92. 

 Such plant-like threads can be collected from the 

 air in damp and unwholesome cellars and rooms, 

 and were at one time supposed to be connected 

 with the production of that fearful disease, the 

 cholera. It has been rendered, however, exceed- 

 ingly probable that all these appearances are but 

 different forms of the fungus which produces 

 common mould, and which is known by the name 

 gf Penidllium glaucum. This fungus is represented 



