34 



BEHAVIOR OF THE LOWER ORGANISMS 



water from the protoplasm (plasmolysis). The reaction of bacteria 

 might then be due to this physical effect of strong solutions. 



If the repellent effects of strong chemicals are due to their osmotic 

 pressure, then all solutions having equal osmotic pressure must be 

 equally repellent. This gives a method of testing the matter. Bacteria 

 have been subjected to the action of many chemicals in solutions of 

 equivalent osmotic pressure, with the following results. There are many 

 strong chemicals which cause reaction when the osmotic pressure is very 

 low, — much lower than in the weakest solutions required to produce 

 reaction in other substances. Such are, as a rule, the strong mineral 

 acids and alkalies (Pfeffer) ; such are potassium cyanide, potassium 

 oxalate, sodium carbonate, sodium sulphite, and potassium nitrate in 

 the experiments of Massart (1889). The reactions produced by these 

 substances can be due then only to their chemical effects, without re- 

 gard to the osmotic pressure. On the other hand, Massart has shown 

 that in two species of bacteria — Spirillum undula and Bacterium me- 

 gatherium — the repellent power of a large number of chemicals is pro- 

 portional to the osmotic pressure of the solutions. It appears probable 



therefore that the osmotic press- 

 ure is the cause of the reaction. 1 

 In certain other bacteria it has 

 been demonstrated that there 

 is no such sensitiveness to os- 

 motic pressure. Bacterium termo 

 enters the strongest solutions of 

 attractive salts. This is sup- 

 posed to be because its proto- 

 plasm is permeable to the salts 

 in question. Taken all together, 

 the experimental results demon- 

 strate that in many cases the 

 negative reaction is due to the 

 chemical properties of the sub- 

 stance, and they render it probable that in some other cases the reaction 

 is due to the osmotic pressure. 



It is not always more concentrated solutions that cause the reversal 

 of movement. Bacteria that live in sea water keep out of areas of dis- 



Fig. 29. — Repulsion of Spirilla of sea water 

 by distilled water. The upper drop consists of 

 sea water containing Spirilla; the lower of distilled 

 water. At x these have just been united by a 

 narrow neck. At y and z the bacteria are driven 

 back before the advancing distilled water. After 

 Massart (1891). 



1 This conclusion is weakened by the fact that the bacteria are much less repelled by sev- 

 eral substances — glycerine, asparagine, dextrose, and saccharose — even when they are so 

 concentrated as to have higher osmotic pressure than the repellent solutions of the substances 

 above mentioned ( Massart, 1889). This is explicable only by making certain special, un- 

 proved assumptions for each case. The matter needs further investigation. 



