CONDITIONS OF GROWTH. 121 



While many species grow in various media and under various 

 conditions of temperature, etc., others are greatly restricted in this 

 regard ; thus Bumm only succeeded in cultivating the gonococcus 

 upon human blood serum, and even upon this was not able to 

 carry it through a series of successive cultures. It is very probable 

 that certain species can only grow in association with others which 

 elaborate products necessary for their development. 



Substances favorable for the growth of a particular species may 

 restrain its development if present in too large an amount. Thus 

 the phosphorescent bacilli multiply abundantly in a nutrient solution 

 containing 2. 5 per cent of sodium chloride ; but this amount would 

 restrain the development of some other species, and a considerable 

 increase in the quantity of salt prevents the growth of all microor- 

 ganisms. In the same way the addition of two per cent of glucose 

 to culture solutions is favorable for the development of certain spe- 

 cies, and especially for the anaerobic bacteria ; but a concentrated 

 solution of the same substance prevents the growth of all bacteria. 



The influence of one species upon the growth of another has 

 been studied by various bacteriologists, and especially by Sirotinin 

 and by Freudenreich. When several species are associated in the 

 same culture one may take the precedence and the others may de- 

 velop later ; or two or more species may develop at the same time ; 

 or the growth of one species may prevent the development of an- 

 other, either () by exhausting the pabulum necessary for its growth 

 or (b) by producing substances which inhibit the development of an- 

 otlier species or destroy its vitality. 



Freudenreich found, as a result of his numerous experiments, 

 that the following species cause a change in bouillon which renders 

 it unfit for the growth of other species : Bacillus pyocyanus, Bacillus 

 cyanogenus, Bacterium phosphorescens, Bacillus prodigiosus, Spi- 

 rillum cholerse Asiaticse. The following species do not cause such a 

 change in bouillon as to render it unfit for the growth of other spe- 

 cies : Bacillus typhi abdominalis, Bacillus anthracis, Bacillus septi- 

 caemia? hsemorrhagicEe, Spirillum tyrogenum. The following have a 

 decided antagonism : Bacillus pyogenes foatidus prevents the growth 

 of Spirillum choleras Asiaticae ; Micrococcus roseus prevents the 

 growth of Micrococcus tetragenus. The cholera spirillum will not 

 grow in sterilized cultures of Bacillus pyocyanus, or in bouillon 

 which has served for a previous culture of the same microorganism 

 (Kitasato). Other bacteria which fail to grow in bouillon which 

 has already served for the cultivation of the same species are Bacil- 

 lus typhi abdominalis, Bacillus cyanogenus, Bacillus prodigiosus, 

 Micrococcus roseus, etc. (Freudenreich). 



