The Conditions of Life and Death. 91 



tions, come to extinction. But this isolation is hardly a 

 natural condition, and was not included in Weismann's 

 doctrine. Nor, of course, does he deny the violent 

 death of Protozoa. 



(3) Thirdly, it is worthy of note that at least many 

 Protozoa are not subject to death from bacterial infec- 

 tion to the same degree as higher animals. The Amoeba, 

 for instance, seems but little perturbed by the presence 

 of various virulent microbes. It engulfs them and di- 

 gests them, as the phagocytes of higher animals do 

 when in vigorous health, or when the odds against 

 them are not too strong. 



Assuming, then, that the simplest organisms are not 

 subject to death in the same degree as higher animals 

 are, what of immortality in the latter? 



The only biological contribution to this question, 

 which has of course nothing whatever to do with the 

 religious conviction of spiritual immortality, is the doc- 

 trine of the organic continuity of the germ-cells or germ- 

 plasm, which many have spoken of as immortal. 



Weismann has made this conception most precise, 

 but it has been in the minds of many. Goebel quotes 

 this fine expression of it from Sachs: "That which has 

 maintained itself alive, and has continually reproduced 

 itself since the beginning of organic life upon the earth, 

 moving steadily onward in the eternal change of all 

 structures, in the unvarying alternation of life and 

 death, that is the embryonic matter of vegetation, and 

 it is this which in certain cases differentiates itself into 

 the two sexes in order again to unite". 



The forms of life are so varied that there is almost no 

 corner of the earth or sea where it would be safe to pre- 

 dict the absence of organisms. On the moun- General 

 tain top and the floor of the deep sea, on the Conditions 

 polar snow and in the desert sand, in the of Llfe ' 

 Mammoth Cave and in the Great Salt Lake, in the hot 

 spring and in the polar water, almost everywhere we 

 find life. It might, perhaps, be called a modern 

 achievement, the demonstration of the almost universal 

 distribution of organisms upon the earth, and the 

 recognition of that protean plasticity which enables 



