32 BEHAVIOR OF THE LOWER ORGANISMS 



formed in food substances ; meat extract, for example, is an agent which 

 produces such collections in most species of bacteria. Pfeffer (1884) 

 found that Bacterium termo forms collections in meat extract, aspara- 

 gine, peptone, white of egg, conglutin, grass extract, leucin, urea, and 

 various other substances which might serve as nourishment. The 

 so-called sulphur bacteria use hydrogen sulphide in their nutritive pro- 

 cesses, and are found to collect in solutions of this substance (Miyoshi, 

 1897). 



Many bacteria collect also in solutions of chemicals which probably 

 do not serve directly as food. 1 Bacterium termo collects markedly in 

 weak solutions of potassium carbonate, so that this is a favorable sub- 

 stance for demonstrating the collections. It collects also in most salts 

 of potassium, and in a less marked way in many other inorganic chem- 

 icals. Indeed, this species may be said to gather in weak solutions of 

 most inorganic chemicals, save in those of the powerful acids and alka- 

 lies. This bacterium lives on decaying vegetation, from which many 

 chemicals diffuse into the surrounding water ; potassium salts especially 

 are given off in this manner. The tendency of the organisms to collect 

 in such salts therefore keeps them in proximity to the decaying vegeta- 

 tion which serves them as nourishment ; these reactions are thus indi- 

 rectly adaptive. But Bacterium termo collects in certain chemicals that 

 are not thus given off by decaying vegetation. Pfeffer (1888) found that 

 they gather in salts of rubidium, caesium, lithium, strontium, and 

 barium, with which under natural conditions they never come in con- 

 tact. It has been suggested that this may be explained as due to a simi- 

 larity in the effect of these chemicals to the effects of others which they 

 do meet under natural conditions. The organisms react thus in the 

 same way to similar stimulation, without regard to its diverse source in 

 different cases. 



Many other bacteria resemble Bacterium termo in collecting in solu- 

 tions of a great variety of chemicals. Miyoshi (1897) found that the 

 sulphur bacterium Chromatium weissii forms collections in weak solu- 

 tions of hydrogen sulphide, potassium nitrate, ammonium nitrate (Fig. 

 28), calcium nitrate, sodium-potassium tartrate, ammonium phosphate, 

 monosodium phosphate, sodium chloride, cane sugar, grape sugar, 

 asparagine, and peptone. 



Some reactions can hardly be considered in any way adaptive. 

 Rothert (1901) found that Amylobacter and another bacterium collect 



1 The method of testing the reaction to chemicals has usually been as follows. A capillary 

 glass tube is filled with the solution to be tested, and one end is sealed. The open end is 

 then brought into the fluid containing bacteria ; these then enter the tube (Fig. 28) or leave 

 it empty (Fig. 24, .-/), depending on their reaction to the chemical. 



