EFFECTS OF CARBON DIOXIDE aA 
physiological characters of many of the bacteria, a group in 
which, for obvious reasons, our physiological knowledge has far 
outstripped our morphological knowledge. Botanists have also 
accumulated an enormous fund of knowledge relating to the com- 
parative physiology of the green plants, while in such special 
fields as the study of the blood sera of the higher vertebrates, to 
give but one example, encouraging progress has been made. 
Nevertheless, it is apparent that very little has been done in the 
way of systematic studies along the lines suggested, with the ulti- 
mate object of making the physiological characters of each organ- 
ism as well known as its morphological ones. Su¢h an under- 
taking is not the work of one man or of one generation. Many 
years must elapse before our knowledge will be anything but 
exceedingly fragmentary and scattered. The following paper 
is therefore a very modest contribution to so large a subject. It 
deals merely with the effects of a single common and important 
substance, carbon dioxide, on a number selected protozoan forms, 
with especial reference to their movements and general vitality. 
It will be followed at intervals by other papers on the effects of 
various other substances, so far as possible on the same forms. It 
is not claimed that the results are, or will be, complete or exhaus- 
tive; still it is hoped that they may not be without interest and a 
certain amount of value. | 
II. MATERIAL AND METHODS 
The forms studied were various of the most common ciliate 
Infusoria and flagellates, i.e., Paramecium caudatum, P. aurelia, 
P. bursaria, Colpidium colpoda, Coleps hirtus, Blepharisma 
lateritia, Euplotes patella, Vorticella nebulifera, Peranema tri- 
chophorum, Euglena viridis (?), Chilomonas paramecium, and 
Entosiphon suleatum. In the case of all the forms mentioned 
except the last one, observations were made on individuals from 
several different cultures of different origin, the intention being 
to obtain, so far as possible, data which would apply to the species 
as a whole and not simply to a particular race. Of course it will 
be necessary to extend the observations still further before draw- 
