Ejjcct of Chemicals on Growth ^31 



found that in no case did the presence of an)' of the chemicals 

 in the hay infusion stop the normal growth of the bacteria, the 

 culture medium with the chemical in it becoming turbid with 

 bacteria at about the same time as the control hay infusion. For 

 this reason there will be about the same amount of food in one 

 culture medium as the other, and the question of food affectmg 

 the general results will be negligible. 



SUMMARY AND DISCUSSION 



1. The investigations do not show that any of the substances 

 studied have what could be called a specific or characteristic effect 

 on growth. When very weak they have no effect whatever. 

 In greater concentrations, all retard the later stages of growth, 

 at the same time manifestly interfering with the other vital 

 processes of the organism. When still stronger even the early 

 stages of growth are impeded or prevented; in such cases the organ- 

 ism is quickly killed by the chemical. In no case is the growth 

 affected without other injury to the organism. On the whole it 

 appears clear that the effects on growth are secondary; they are 

 consequences of the interference of the chemical with the other 

 vital processes of the animal, and do not appear unless such inter- 

 ference exists. Essentially the same effects on growth appear 

 whether the interference with other vital processes is due merely 

 to the absence of any salts in the medium, to the presence of undue 

 quantites of such a common substance as sodium chloride, or 

 of minute quantites of such poisons as nicotine, alcohol or strych- 

 nine. None of the substances studied, whatever the amount 

 present, has a tendency to increase the normal rate or amount of 

 growth (although the presence of a small amount of sodium chlo- 

 ride permits this normal growth to occur, when it otherwise would 

 do not soj. 



2. The early stages of growth show in certain respects a remark- 

 able independence of the surrounding medium. In many cases, 

 as we have seen, a certain amount of growth takes place under 

 conditions which later destroy the organism. At fission the organ- 

 ism seems to' have a certain potential of growth, due largely to 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 8, NO. 4. 



