PHYSICAL PEOPEETIES OF PEOTOPLASM 21 



This simple fission of a single protoplasmic unit, or cell, forms, 

 as we shall see later on, the essential feature of ordinary repro- 

 duction throughout the animal and vegetable kingdoms. It will 

 be observed that in this process generation succeeds generation 

 without the intervention of anything which we can speak of as 

 death. There is indeed no room for death in the history of 

 these simple organisms, unless it be death by accident, for every 

 time fission takes place the entire body is used up, and nothing is 

 left over to die. Nor is there any distinction to be drawn between 

 parent and offspring, for the two new individuals are in all 

 respects similar to one another, and neither can be said to precede 

 the other in point of time. 



We have now become sufficiently well acquainted with the 

 nature of protoplasm to profit by a more detailed examination of 

 its physical and chemical properties. We have seen that, as it 

 occurs in the body of an Amoeba, it is a viscid, more or less 

 liquid, colourless substance, almost transparent but exhibiting, 

 under moderately high powers of the microscope, a granular 

 appearance due to the presence of numerous minute and more or 

 less opaque particles. These particles may be regarded as 

 impurities, and indeed protoplasm can never be obtained in a 

 perfectly pure state, for it is constantly undergoing chemical 

 change, both constructive and destructive, and the impurities 

 owe their origin partly to the food materials which are taken in 

 and partly to katabolic processes which give rise ultimately to 

 waste products. 



Even apart from these impurities, however, the protoplasm 

 itself never exhibits a perfectly uniform structure. It is by no 

 means homogeneous but shows a more or less distinct differentia- 

 tion into different portions, as, for example, into nucleoplasm and 

 cytoplasm, ectoplasm and endoplasm, and so forth. In other 

 words it is an organized substance. Moreover, it has a character- 

 istic minute structure or texture which can to some extent be 

 recognized under high powers of the microscope and concerning 

 the interpretation of which different observers are as yet by no 

 means all agreed. According to Professor Biitschli it is a kind 

 of microscopic foam, consisting of exceedingly minute drops of 

 a more liquid substance separated by very thin layers of denser 

 material, and thus resembling physically such a foam as can 

 be prepared from a mixture of oil, salts of various kinds, and 



