CHAPTER VI 



RESPIRATORY METABOLISM 



Theodore Louis Jahn 



Studies of the respiration of the Protozoa have, for the most part, 

 been fragmentary, and our information on the subject resembles an ac- 

 cumulation of a number of more or less isolated data, rather than a 

 unified body of knowledge. This situation is due to a variety of causes, 

 chief among which is probably the fact that most studies of respiration 

 have been made by physiologists who chose, among the members of the 

 animal kingdom, the organisms which seemed to be the most suitable 

 for a particular type of experiment. From this viewpoint the study of 

 protozoan respiration has suffered a severe handicap, in that a consider- 

 able mass of protozoan protoplasm, free from bacteria and other organ- 

 isms, has not always been easy to obtain, and in that our methods for 

 measuring very small rates of respiratory exchange have not been nearly 

 as accurate or as convenient as we might desire. However, with gradual 

 technical advances, it seems probable that in the near future we shall see 

 the development of an organized account of protozoan respiration, and 

 it also appears probable that this development will take place among 

 investigators who are primarily interested in the Protozoa. Therefore, 

 it seems advisable to combine a review of data on protozoan respiration 

 with a discussion of the general problems of respiratory metabolism in 

 other biological materials, and to outline for the student not thoroughly 

 trained in the lore of respirometry some of the purposes, methods, and 

 possible interpretations of such a study. 



Among the Protozoa, the intake of oxygen does not require compli- 

 cated respiratory mechanisms. Apparently diffusion, high rate of water 

 exchange, and protoplasmic movements (cyclosis, amoeboid streaming, 

 and "metabolic" movements) are sufficient to maintain a suitable level 

 of O2 tension in the protoplasm and to prevent the accumulation of toxic 

 amounts of CO2. The mechanisms which are responsible for protoplasmic 

 movements and the high rate of water exchange are more properly treated 



