CHAPTER 11. 



PHYSIOLOGICAL ACTIVITIES OF THE PROTOZOA. 



Ehrenberg, in 1838, entitled his monimiental work on the protozoa 

 Die Infuslonsthierchen als vollkommene Organismcn (The Infusoria 

 as Complete Organisms). Despite the great improvements that had 

 been made in the microscope, and the vast collection of facts that 

 had accumulated in connection with the structures of the protozoa, 

 Ehrenberg's point of view was but slightly advanced beyond that of 

 Leeuwenhoek one hundred and fifty years before. "Animalcula," 

 said Leeuwenhoek, " which swim in stagnant waters, and which are no 

 longer than the tails of the spermatic animalcula, are provided with 

 organs similar to those of the highest animals. How marvellous 

 must be the visceral apparatus shut up in such animalcula!" Ehren- 

 berg sought to make out the various organs in this "visceral complex," 

 and with great ingenuity managed to find digestive tract, kidney, brain, 

 heart, ovary, and other organs characteristic of metazoa. The red, 

 so-called "eye spots" were regarded by him as eyes, and the colorless 

 lens upon which they frequently lie was interpreted as a cerebral 

 ganglion, or brain. The contractile vacuole became, for him, a beat- 

 ing heart, and the collecting canals formed the vessels. The macro- 

 nucleus was an ovary, the gastric vacuoles stomachs, while various 

 chance inclusions were regarded as organs of one kind or another. 



While Leeuwenhoek's and Ehrenberg's interpretation made out 

 these primitive animals as marvels of creation in miniature, how much 

 more marvellous are the facts as we know them today and summed 

 up in the statement that the functions of all of these organs of the 

 highest animals are performed within the single cell! The protozoon 

 has no digestive tract, but it seizes food, digests and assimilates it, and 

 grows in size through the addition of such food. It has no heart or 

 circulatory system, and yet it distributes the digested food throughout 

 the body, takes in oxygen, and throws off carbon dioxide as does every 

 many celled animal. It has no kidney, but disposes of the waste 

 matters of oxidation none the less, and so every function of the highest 

 metazoa finds its counterpart in the vital activities of the primitive 

 forms. Nor is the importance of these simpler processes of the proto- 

 zoa any the less, in that they come very close to the ordinary physical 

 and chemical processes that we are familiar with in non-living matter. 

 As complete organisms, therefore, in a sense quite dift'erent from that 



