32 FUNDAMENTAL PROPEETIBS 



le Dantec very properly insists, so many evidences pointing to 

 the conclusion that the varieties of protoplasm in these elementary 

 organisms are almost endless.' 



The capability shown by unicellular organisms of being attracted 

 by food-stuifs was first carefully studied by Stahl in 1884, but 

 according to A. Fischer,'^ " At about the same time Pfeffer inves- 

 tigated from a more general chemical standpoint the effects of 

 such stimuli upon the movements of bacteria, protozoa, and the 

 spermatozoids of the higher cryptogams, and was able to show 

 that the nutritive value was not the sole and only determinant, but 

 that other more recondite factors were involved, factors based on 

 the chemical constitution of the substance employed as a stimulant. 

 For this reason he introduced the now generally adopted expression 

 Chemotaxis." 



Pfeffer's experiments were conducted in a very exact manner. 

 He introduced solutions of different materials, varying in their 

 degrees of concentration, into very short capillary tubes closed at 

 one extremity. A tube thus prepared was then immersed in a 

 drop of the fluid containing the plastides whose behaviour was to 

 be examined. Owing to the capillary bore of the tube diffusion of 

 the fluid only takes place at its orifice, and then slowly. Let us 

 suppose it to have been charged with a solution of peptone, and 

 then immersed in fluid containing Bacteria, which it should be 

 understood are simple cytodes that move by means of cilia as do the 

 swarm-spores of Vaucheria already referred to. The results of 

 this and other experiments are thus referred to by Fischer : — " In 

 five or ten seconds it can be seen that the bacteria are more thickly 

 congregated around the open end of the capillary than elsewhere, 

 and in a few minutes they form a dense swarm there, and begin to 

 enter the tube. The movements of the bacteria in the drop 

 become more lively as soon as the diffusing peptone reaches them, 

 and at the entrance of the tube they are a whirling, 'buzzing' mass, 

 like hiving bees. The potential energy of the food-stuff has been 

 converted into the kinetic energy of the vibrating cilia. If now 

 a cover glass be laid upon the drop another kind of Chemotaxis can 

 be observed. The bacteria which have entered the tube move 

 upward, attracted by the air in the blind end, and in about half an 

 hour that section of the capillary immediately below the bubble is 

 plugged by a thick mass of organisms. But these phenomena, the 



" Loc. cit. pp. 31, 43, 54, 61. 



' "The Structure and Functions of Bacteria," Transln., 1900, p. 78. 



