6 The American Naturalist. [January, 



lesson of our ignorance has not been learned by biologists. 

 We encounter, not infrequently, the assertion that life is 

 nothing but a series of physical phenomena ; or, on the other 

 hand, what is less fashionable science just now, that life is 

 due to a special vital force. Such assertions are thoroughly 

 unscientific ; most of them are entirely, the remainder nearly 

 worthless. Of what seems to me the prerequisites to be fulfilled 

 before a general theory of life is advanced, I have written 

 elsewhere. 5 



II. Conception of Death. 



My thesis reads : There are two forms of death. These are 

 first, the death of the single cells ; second, the death of multi- 

 cellular organisms. Death in the one case is not homologous 

 with death in the other. 



Weismann assumed the complete homology of the two 

 forms of death. Without this assumption, his hypothesis of 

 the immortality of unicellular organisms falls to the ground 

 and with it falls the entire superstructure of his speculations 

 upon germ plasm. Oscar Hertwig (Zeit und Strcitfragen, Heft 

 1) has already expounded, very clearly, the dependence of the 

 theory of germ plasm upon the hypothesis of unicellular im- 

 mortality ; it would, therefore, be superfluous to discuss it 

 here. 



The conception of the biological problem of death, to which 

 I still hold, was formed several years before Weismann's first 

 publication, which appeared in 1882, with the title, " Ueber die 

 Bauer des Lebens." He has further defended his view in his 

 article, " Ueber Leben und Tod " (1884), and has steadfastly ad- 

 hered to it since. In the years 1877-1879 I published my 

 theoretical interpretation of the problem. 6 This interpretation 

 became the starting point of elaborate special investigations, 

 by which I endeavored to advance the solution of the problem 

 and, in fact, observation and experiment have confirmed the 



5 C S. Minot, On the conditions to be filled by a theory of life, Proc Amer. 

 Assoc. Adv. Sc., XXVIII, 411. 

 6 Proc. Boston Soc. Nat. Hist., XIX, 167 ; XX, 190. 



