Mat 3, 190.'] 



SCIENCE 



695 



growth and decline, on the causes of old 

 age and natural death, and many others. 

 There is not one of these questions that can 

 be adequately considered apart from the 

 phenomena exhibited by the protozoa. It 

 is my impression that we are more likely to 

 solve these problems, in so far as they can 

 be solved, by studies on the protozoa than 

 by investigation on the higher forms. 

 Some of the researches in this field have 

 definitely brought into the arena of scien- 

 tific ■ experiment and discussion the old 

 dream of the alchemists of the artificial 

 prolongation of life, perhaps of human life. 

 If this is no longer a fantastic vision of 

 pseudo-science but has won a place among 

 the legitimate subjects of scientific inquiry, 

 it is in no small measure owing to investi- 

 gations on the protozoa. 



If we turn for a moment to the study of 

 heredity and evolution, here again it was 

 in considerable measure a comparison of 

 the life histories of protozoa with those of 

 metazoa that necessitated a readjustment 

 of many views that had long been held, 

 almost without question, as applicable to 

 the higher forms of life. Considerations 

 on reproduction and the duration of life in 

 protozoa formed the starting point of "Weis- 

 mann's inquiries on heredity that resulted 

 in a total denial by him of the inheritance 

 of acquired characters in higher organisms 

 —a supposed factor that formed an impor- 

 tant part of Darwin's general theory and 

 was the very corner-stone of Herbert 

 Spencer's philosophy of organic nature. 

 Whether Weismann was right remains to 

 be seen. Naturalists are still in disagree- 

 ment as to whether acquired characters are 

 inherited or not. But there can be no 

 doubt that Nussbaum and Weismann al- 

 tered our whole point of view by fixing 

 attention on the fact that heredity is ef- 

 fected in metazoa, as in protozoa, by cell- 

 division; that just as protozoa inherit the 



characteristics of the mother cell because 

 directly derived from it by division, so the 

 body of the higher animal inherits not from 

 the body of the parent but from the egg, 

 because derived from it by division. This 

 simple fact, while it places the basis of 

 heredity in its true light, enormously in- 

 creases the difficulty of accepting the in- 

 heritance of acquired characteristics of the 

 body. That such an inheritance of ac- 

 quired characters is difficult to conceive 

 does not, of course, prove that it is not a 

 fact; but the arguments urged by Weis- 

 mann were of such force as to demonstrate 

 the imperative need of a reexamination of 

 the whole question. The illuminating view 

 of heredity brought forward by Nussbaum 

 and Weismann, primarily suggested, I re- 

 peat, by the mode of reproduction in pro- 

 tozoa, has made a deep mark on biological 

 research, and has led to reinvestigation of 

 many conclusions that had naively been 

 taken for granted, with no realizing sense 

 of the formidable difficulties that they in- 

 volved, or the weakness of the evidence on 

 which they had been based. Thus the study 

 of the protozoa has had its effect on every 

 part of biology that is concerned with ques- 

 tions of historical descent; and I do not 

 think it forced to say that these creatures 

 may have something to teach us in every 

 department of thought into which evolu- 

 tionary considerations enter. 



It was Weismann 's view that the proto- 

 zoa are endowed with never-ending life. 

 From the physical point of view, this con- 

 clusion was not altogether well founded, at 

 least in the sense in which he meant it; 

 but metaphorically speaking it was true. 

 They certainly possess a vitality that seems 

 vidthout limit as a power to animate scien- 

 tific research, to invade new fields of dis- 

 covery. Their latest achievement is an 

 irruption into the domain of pathology, 

 and the inroads they have already made are 



