EARLY HISTORY OF LIFE 



37 



mission of these characteristics from par- 

 ents to offspring is known as heredity; just 

 how this is done has stimulated biologists 

 in recent years to search for the explana- 

 tion at the level of molecules. The search 

 has been fruitful, as we shall learn a little 

 later. 



PROTOPLASM AND LIFE 



If the characteristics of living things are 

 to be understood, it is necessaiy to study 

 the physical material in which life resides. 

 This material was observed by early biolo- 

 gists and was given the name protoplasm 

 by Purkinje over 100 years ago. The word 

 means the first form (protos — first, plasma 

 — form). If tiny pieces of any plant or 

 animal are examined with a microscope, 

 they will be found to be composed of cells, 

 each of which contains protoplasm. There- 

 fore, a study of this material is essential if 

 much useful information is to be had about 

 what life is and how it tvorks. We do not 

 have the answer to the first of these ques- 

 . tions at present, but some progress is being 

 made on the second. If and when the an- 

 swers do come, they will probably come 

 from a study of protoplasm itself. 



Recalling our earlier discussion of the 

 origin of life, it must be concluded that 

 protoplasm is very complex. It is so deli- 

 cately adjusted physico-chemically that any 

 attempt to find out how it behaves or of what 

 it is made means immediate loss of the very 

 thing sought for. It can be handled only 

 with utmost care without killing it. A dead 

 animal no longer possesses protoplasm, be- 

 cause by definition protoplasm encompasses 

 that "something" called life. Biologists are 

 not interested in "something," rather they 

 are concerned with the underlying princi- 

 ples that explain life. What protoplasm is 

 composed of, how these materials are or- 

 ganized in the cell and the body, and how 

 they interact with one another to generate 

 that which is referred to as life, are among 

 the most fundamental questions which the 



biologist is seeking to answer. While the 

 problem at the outset appears to be insur- 

 mountable by its very nature, some progress 

 has been made by employing the methods 

 of the chemist and physicist. Today a great 

 deal is known about protoplasm, but there 

 is much more to be learned before a com- 

 plete understanding of life can be had. 



HOW DOES PROTOPLASM LOOK? 



The superficial examination of any living 

 thing reveals a more or less homogeneous 

 surface to the naked eye. If, however, small 

 thin pieces are removed and placed under 

 the microscope, an entirely different pic- 

 ture is seen. The over-all pattern of tiny 

 repeated units, cells, is the most striking 

 impression that one gets. Now, if one of 

 these cells is observed with the highest 

 power of the microscope, some of the visi- 

 ble features of protoplasm can be detected. 

 It would not matter what cells we used for 

 this study; they would all include proto- 

 plasm, which would appear remarkably 

 alike in all of them. This fact was learned 

 by the early biologists, which convinced 

 them that protoplasm formed the "physical 

 basis of life," a statement with which we 

 fully agree today. One never finds life re- 

 siding anywhere but in protoplasm, with 

 the possible exception of the controversial 

 viruses. 



Since all cells are very similar in respect 

 to their protoplasmic content, let us select 

 a large animal cell for study. Amoeba, a sin- 

 gle-celled animal, will do very well because 

 it is huge as cells go and its parts can be seen 

 very easily under an ordinary light micro- 

 scope (Fig. 2-16). The general impression 

 that one gets from observing this tiny ani- 

 mal is that its protoplasm is grayish in color 

 and is usually moving about within the 

 limits of the organism. The cell crawls 

 about by sending out projections, called 

 pseudopods (false feet). Such a pseudopod 

 forms by forcing out a clear watery lobe 

 which is immediately followed by granular 



