52 CHEMICAL AGENTS AND PROTOPLASM [Cn. I 



Experiments on cliemotaxis show that many substances 

 brought near to protoplasmic bodies control their locomotion. 

 The effect upon locomotion depends both upon the kind of 

 protoplasm and the strength of the reagent. In many cases, 

 a certain strength of reagent attracts an organism, while a 

 stronger solution repels, and a weaker solution is indifferent. 

 In such a case we may speak of the protoplasm as being attuned 

 to the attracting strength of the reagent. We find great diver- 

 sity in the strength of solution of a reagent to which different 

 protoplasms are attuned. This difference of attunement to 

 chemotactic reagents is parallel to the difference in strength of 

 the killing solution of various protoplasms. As the latter is 

 probably due to the past action of chemical agents upon the 

 protoplasm, so is also the former. 



APPENDIX TO CHAPTER I 



Cytotaxis ( = Cytotropism) 



Roux ('94) has given the latter name to a phenomenon which 

 is probably only a special case of cliemotaxis, but which may be 

 better considered apart. He isolated, in an indifferent medium, 

 two or three cells from the egg of a frog (Rana fusca) at the 

 morula or blastula stage of development. These he placed near 

 each other upon a glass slide, and found that they moved slowly, 

 and that the direction of the movement of any one cell was, 

 under certain conditions, determined by the position of the 

 other cell or cells. 



In order to perform the experiment a proper medium in which to study 

 the movement of the cells must be prepared as follows : a small quantity 

 5 to 10 ccm. of fresh egg albumen (not cut up, but with the albumen 

 threads intact) is filtered through clean wadding, and the completely clear 

 filtrate is used. In other cases a more or less strong salt solution is 

 employed. The cleavage cells are isolated in the filtrated albumen, on a 

 glass plate, by means of needles. To diminish evaporation the glass plate 

 is put into a shallow glass vessel containing several drops of water. 



When two cells were placed near each other (about one-fourth 

 of their diameter apart), the distance between them diminished. 

 The approach took place along a line joining the two cells ; 



