84 ALBUMINOUS MATTERS. 



the decomposing liquid, and produce in it, by their vegetative activity, 

 the changes of putrefaction. These cells belong to the genus " Bacteri- 

 um," so called from their simple rod-like form ; and the species which 

 is invariably to be found in putrefying infusions is known by the 

 name of Bacterium termo. The cells are of an oblong form, and 

 average 3 mmm. in length by 0.6 mmm. in thickness. They are usually 

 double, consisting of two single cells placed end to end. While actively 

 growing in a putrefying infusion, they are in constant process of mul- 

 tiplication, by which their numbers are rapidly increased. The multi- 

 plication takes place by spontaneous division of the cell, by a trans- 

 verse partition which grows across its middle. After a time the two 

 cells, thus formed out of a single one, separate from each other, and 

 each repeats the process for itself. 



One of the most remarkable characters of the bacterium cells is 

 their active spontaneous movement. During a certain period of their 

 development they are in incessant and rapid motion by means of a 

 conical rotation about their longitudinal axis, by which they are trans- 

 ported in various directions through the fluid in which they are contained. 

 This motion is often so rapid that it can hardly be followed by the eye ; 

 in other instances it is so slow that its mechanism may be distinguished 

 by careful examination. The movement and mutiplication of the bac- 

 terium cells go on while putrefaction continues. After all the albumin- 

 ous ingredients of the infusion have been decomposed, the liquid again 

 becomes clear, and the bacterium cells subside to the bottom in a quies- 

 cent whitish layer. A small portion of this layer will readily excite 

 putrefaction, if added to another albuminous liquid. 



As the bacterium cells effect the decomposition of albuminous matters 

 by their own vegetative activity, it is for this reason that putrefaction 

 is limited by certain special conditions, already mentioned. Bacteria 

 belong to the group of colorless cryptogamic vegetables. Like other 

 plants of this kind, they assimilate directly organic substances ready 

 formed, and at the same time absorb oxygen and exhale carbonic 

 acid, after the manner of animals. Consequently oxygen is one of the 

 substances essential to their growth ; and, as putrefaction takes place 

 only by means of their vital activit} r , ox}^gen or atmospheric air must 

 be present in order to allow putrefaction to go on. Furthermore the 

 presence of moisture is necessary to their growth, as it is to that of all 

 other plants ; and a substance thoroughly dried cannot putrefy, since no 

 vegetative development is possible in the total absence of moisture. A 

 certain degree of warmth is also essential to the continued growth of 

 these bodies. Their development is suspended by a freezing tempera- 

 ture, and their vitality is destroyed by prolonged contact with boiling 

 water. 



Lastly, a certain amount of albuminous matter is necessary for the 

 nutrition of bacteria. Their cells may remain indefinitely, in a quies- 

 cent condition, suspended in other fluids or even in pure water; but 

 for their active development and multiplication they require the pre- 



