540 MERKEL HENRY JACOBS 
solutions, or in solutions of chloroform or ether, which prevent 
completely all muscular movements. Recently Mayer (’11) has 
found that the effects of many ions on ciliary and muscular move- 
ments are exactly opposite those that depress the one stimulating 
the other. He found that the ciliary movements of trochophore 
larvae at first cease in water charged with carbon dioxide but 
later start again. It is well known that carbon dioxide at first 
stimulates and later depresses muscular movements in the higher 
vertebrates (Lee, ’07). In Vorticella in the same cell this antag- 
onistic action appears very clearly. In other forms it is harder 
to demonstrate a primary depression of ciliary activity, possibly 
because of the response of the organism as a whole in an adaptive 
way. In Chilomonas, however, the primary depression of the 
movements of the flagella nearly always occurs. 
V. SUMMARY 
1. Each of the twelve forms studied reacts to carbon dioxide 
in a characteristic way and has a characteristic resistance, which 
is highest in Colpidium colpoda, which remains alive many 
hours, and lowest in Coleps hirtus, which is killed in a few minutes. 
A certain amount of individual and cultural variation may occur 
which prevents the expression of the resistance of the species in 
absolute terms. Compared with other forms under the same 
conditions, however, the relative resistance is fairly constant. 
2. Some forms are killed outright very quickly (Coleps hirtus 
and Paramecium bursaria). In others all movements are stopped 
in a few minutes but death occurs relatively late, the powers of 
recovery being high (Euglena). In still others, locomotion ceases 
very promptly but movements of the cilia, flagella, ete., may per- 
sist for a long time (Peranema trichophorum, Euplotes patella, 
etc.). In theremainder, more or less normal locomotion continues 
for a considerable time (most of the ciliates, Chilomonas and 
Entosiphon). The result in all cases, however, if the experiment 
be long enough continued, is cessation of movements and death. 
3. In the same cell the contractile elements are usually quickly 
paralyzed (Vorticella and Peranema) while the vibratile structures 
(cilia, membranelles, flagella) are much more resistant. In some 
