BACTERIA AND THEIR EFFECTS. 



401 



a long period of time, either when cultivated artificially, or when grow- 

 ing spontaneously under natural conditions. 



In this way Billroth, who has published the most recent and, in 

 many respects, the most remarkable work upon the subject, was able 

 to make out the whole series of changes, from the spore to the long 

 filaments, by using for his observations the yellowish mould which 

 formed on the wall of his laboratory, where the water leaked slowly 

 from a loose faucet. At the same time he discovered the nature and 

 importance of certain glistening spherical bodies frequently found in 

 infusions containing bacteria, and called Dauersporen, or durable 

 spores (Fig. 1, g), by Cohn, although he did not think bacteria were 

 developed from them. Billroth demonstrated that these Dauersporen 



Fig. 2. Bactehia and LErTOTHKix Filaments found in a Tuknip-Infusion. 



form micrococci in their interior, which are set free by the bursting of 

 the envelope, and are then capable of multiplication by scission, or 

 of lengthening into bacteria ; also, that they are endowed with great 

 vitality, and are not destroyed by freezing, boiling, or drying. He 

 had some which germinated after they had been kept dry for eight 

 years; and, whenever he wished to make sure of the destruction of 

 the spores contained in his experimental liquids, he heated them to 

 392 Fahr. 



They are formed in the interior of bacteria, and sink to the bottom 

 of the liquid which contains them. The importance of these facts in 

 their bearing upon the question of spontaneous generation, and upon 

 the innumerable repetitions and variations of the experiments with 

 sealed flasks, which have attracted so much attention since Pasteur 

 made them, cannot be over-estimated; for, as Prof. Wyman, of Cam- 

 bridge, says, " The issue between the advocates and opponents of the 

 doctrine in question" (spontaneous generation) "clearly turns on the 

 extent to which it can be proved that living beings resist the action 

 of water at a high temperature." American Journal of Science and 

 Art, September, 1867. 



Bacteria themselves are much more easily affected by heat and 

 cold than are these Dauersporen. Their motions cease when the 

 temperature is reduced nearly to the freezing-point ; but it may be 



VOL. TI. 26 



