80 ■ THE AMERICAN MONTHLY [March, 



Hardening. — Imbed in gum as described. 



Sections. — By microtome ; sections to remain in water 30 

 minutes. 



Staining. — -Bv hsematoxylin and eosine. 



Preservation. — In dammar. 



[M. Boneval does not like Canada balsam as a mounting 

 medium, preferring dammar. Hereafter, whenever the word 

 '•'• balsam " is used it will be understood that the author means 

 dammar, although either balsam or dammar may be employed, as 

 the reader may prefer.] 



[7"f be continued. \ 



The Contractile Tesicle of Parameciiini. 



By albert SCHNEIDER, M. D., 



MINNEAPOLIS, MINN. 



The functions of the contractile vesicle in protozoons are but 

 little understood, in spite of the fact that careful work has been 

 done on them. Doubtless the question will not be fully solved 

 for some time. The cause of the difficulty is probably to be 

 found in the delicate chemical reactions involved. The assertions 

 of earlier zoologists were misleading. Some described the con- 

 tractile vesicle as a sort of *■' waterpump," others as a " heart." 

 Stein mentions the "■ nearly pure water " found in the contractile 

 vesicles, and how " it is forced to the exterior through an opening 

 or openings in the cell-wall." The comparison to a "■ heart" is 

 far fetched and meaningless. Biitchli (iSSi and '82) seems to 

 incline towards Stein's view. One gains but little satisfaction 

 from the present literature on the subject. Though I am not 

 now able to make any conclusive statements, yet I hope to con- 

 tribute something towards solving the mystery. I have made a 

 special study of it. 



I used a ?;-in. Zeiss objective with B. ocular. In order to 

 reduce the activity of the organism, I used CO^, and chloro- 

 form vapor. This was rather unsatisfactory, owing to the care re- 

 quired in admitting the reagent. The slightest excess would soon 

 destroy life. Besides, the conditions were far from normal. A 

 far better method is that suggested by Professor H. F. Nachtrieb, 

 of using a solution of cherry gum just thick enough to render 

 the specimens comparatively inactive. By this method I could 

 keep them alive for hours and study both their movements and 

 the action of the contractile vesicle. The mechanical parts of the 

 experiments I need not describe, as they were very simple. 



As is well known, Paramecium aiirelia has two contractile 

 vesicles located in the ectosarc opposite the ventral side. As a 

 rule, they contract alternately with great regularity. The 

 average time required for a complete pulsation is about one 



