EXCYSTATION 73 



tive headings of Excystation and Reproduction 

 (series A). The latter results appeared to be of 

 such importance that the experiment was repeated 

 (with some slight modifications of technique) as 

 follows : 



An identical series of six test-tubes was made as 

 before (vide Table II., A F). Jelly films were 

 made from each of these on microscope slides, which 

 were then inverted, resting on corks, over water in 

 Petri dishes, sterile precautions being taken through- 

 out. Dead boiled bacteria were smeared on all the 

 films, and a few drops of normal horse serum were 

 placed on A to D, the films thus corresponding 

 exactly to the slopes employed in the former 

 experiment. On this occasion, however, living 

 amoeba* (obtained from cultures which were free 

 from living bacteria) were placed on each jelly 

 film instead of cysts, and a cover-slip was dropped 

 over each preparation. As already described in 

 Chapter I., the cover-slip does not press on the 

 amoebas when the slide is in the inverted position 

 which we have employed, and its use is advisable, 

 since it enables the preparations to be more readily 

 examined. The specimens were examined twice a 

 day for several days and the degree of multiplication 

 is tabulated under the heading Reproduction 

 (series B). 



It has thus been possible to reduce the food 

 supply of the amcebae to a uniform condition, 

 namely dead bacteria and horse serum, and to show 

 the influence of tyrosin in exciting reproduction 

 (tube C) and its increased effect (tube D) when an 

 augmentor (kinetic) such as choline is present. 



At the end of a week, horse serum was smeared 



