VITAL PIIKXOMEXA OF BACTERIA 87 



isolated. Every agent which is injurious to the existence of the bacteria 

 affects this property. Living bacteria are always found in phosphor- 

 escent cultures; a filtered culture free from germs is invariably 

 non-phosphorescent; but while the organism cannot emit light except 

 during life, it can live without emitting light, as in an atmosphere of 

 carbonic acid gas, for instance. They are best grown under free access 

 of oxygen in a culture medium prepared by boiling fish in sea-water 

 (or water containing 3 per cent, sea-salt), to which 1 per cent, peptone, 

 1 per cent, glycerin, and 0.5 per cent, asparagin are added. Even in 

 this medium the power of emitting light is soon lost unless the organ- 

 ism is constantly transplanted to fresh media. 



Thermic Effects. The production of heat by bacteria does not attract 

 attention in our usual cultures because of its slight amount, and even 

 fermenting culture liquids with abundance of bacteria cause no sensa- 

 tion of warmth when touched by the hand. Careful tests, however, 

 show that heat is produced. The increase of temperature in organic 

 substances when stored in a moist condition, as tobacco, hay, manure, 

 etc., is one partly at least due to the action of bacteria. 



Chemical Effects. The processes which bodies being split up undergo 

 depend, first, on the chemical nature of the bodies involved and the 

 conditions under which they exist, and, secondly, on the varieties of 

 bacteria present. A complete description of these chemical changes 

 is at present impossible. Chemists can as yet only enumerate some of 

 the final substances evolved, and describe, in a few cases, the manner 

 in which they were produced. Bacteria are able to construct their body 

 substance out of various kinds of nutrient materials and also to pro- 

 duce fermentation products or poisons, and they are able to do these 

 things either analytically or synthetically with almost equal ease. This 

 ambidextrous metabolic power exists, according to Hueppe, among 

 bacteria to an extent known as yet among no other living things. 



In the chemical building up of their body substance we can distin- 

 guish, as Hueppe concisely puts it, several groups of phenomena: 

 Polymerization, a sort of doubling up of a simple compound; synthesis, 

 a union of different kinds of simple compounds into one or more com- 

 plex substances; formation of anhydride, by which new substances 

 arise from a compound through the 'loss of water; and reduction or 

 loss of oxygen, which is brought about especially by the entrance of 

 hydrogen into the molecule. The breaking down of organic bodies of 

 complicated molecular structure into simpler combinations takes place, 

 on the other hand, through the loosening of the bonds of polymeriza- 

 tion, through hydration or entrance of water into the molecule, and 

 through oxidation. 



The chemical effects which take place from the action of bacteria 

 are greatly influenced by the presence or absence of free oxygen. The 

 access of pure atmospheric oxygen makes the life processes of most 

 bacteria more easy, but is not indispensable when available substances 

 are present which can be broken up with sufficient ease. The standard 

 of availability is verv different for different bacteria. 



