22 MANUAL OF ANIMAL BIOLOGY 



When it comes to the determination of the exact physical struc- 

 ture of protoplasm, whether it be from an Amoeba or from a Man, 

 the problem becomes very difficult — in fact, so difficult that the 

 solution is not apparent at the present time, even though it has 

 been, and still is, the subject of a great amount of investigation 

 by some of the ablest scientists. Scientific investigation with a 

 view to determining the exact details of protoplasmic structure, 

 as has been noted in the preceding chapter, is definitely limited 

 by the fact that protoplasm cannot be subjected to intensive 

 analytical methods without thereby destroying the primary object 

 of the investigation, namely, the quality we call life. The dead 

 material, which was formerly protoplasm, can, of course, be sub- 

 jected to intensive analysis, but such studies have not so far re- 

 vealed the basic secrets of protoplasmic structure. 



B. Life Processes of an Amoeba 



1. Nutrition 



One of the fundamental characteristics of living organisms is 

 the power to take in certain materials from the outside environ- 

 ment and either use them at once to supply energy for the life 

 processes, or convert them into the actual living protoplasm of 

 the body. The nutrition of an animal is designated as holozoic, 

 and it involves destructive chemical processes in which various 

 types of complex foodstuffs are broken down, and the resulting ma- 

 terials utilized in the various ways necessary either for the nourish- 

 ment of the protoplasm or for securing energy for the essential 

 life processes. The Amoeba exhibits a typical holozoic type of 

 nutrition, and this animal has the power to carry on this process in 

 essentially the same way as do the highest types of animal organ- 

 isms, the only difference being that the single-celled animal, lacking 

 the highly developed nutritive systems of the higher forms, does 

 the work with much simpler apparatus. The holozoic nutrition of 

 animals involves several stages, namely, the capture and ingestion 

 of food, its digestion and assimilation, and, finally, the egestion 

 of the indigestible refuse. These various steps in the nutrition of 

 Amoeba may next be considered. 



In the normal environment of the Amoeba there are materials of 

 various kinds which the animal is able to utilize as food. Among 

 these may be noted unicellular plants, such as the Bacteria and 



