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SCIENCE 



[N. S. Vol. XXXIV. No. 866 



gration, as developed by Buffon in France, 

 and Needham in England. These natu- 

 ralists saw in the Leeuwenhoek animaleulse 

 only the disintegrated and free-living 

 parts of higher animals and plants. It 

 can not be stated positively, but there is 

 nevertheless some reason for believing 

 that the smouldering embers of this philo- 

 sophic fire were kept alive by Oken and 

 Goldfuss in Germany, and by Bichat in 

 France and finally fanned into the full 

 blaze of the cell theory by Schleiden and 

 Schwann, ninety years afterwards. 



In the meantime the work of 0. F. 

 Miiller (1786), and especially that of C. 

 G. Ehrenberg (1833-1838) and F. Dujar- 

 din (1835-1841) had resu.lted in some 

 taxonomic order amongst these micro- 

 scopic forms which Ciivier had gener- 

 ously included in the animal kingdom 

 under the name of chaos animalcule. 

 Other important steps were taken by von 

 Siebold in 1845 who first described proto- 

 zoa as single-celled organisms; by Max 

 Schultze in 1863, who showed that the liv- 

 ing substance "sarcode" of protozoa is the 

 same as the living substance ' ' protoplasm ' ' 

 of higher animals; and by Biitschli in 

 1875 who gave the final evidence in sup- 

 port of the unicellular nature of protozoa 

 by showing that the nucleus of the proto- 

 zoan cell is similar to that of the tissue or 

 egg cell, and like the latter, divides by 

 karyokinesis. 



Biitschli 's later work of 1882-88 gave 

 the real ground work on which modern 

 protozoology rests. Summarizing all of 

 the preceding discoveries and bringing to- 

 gether the disconnected observations and 

 theories of his predecessors, he gave us in 

 these approximately 1,700 pages of acute 

 criticism careful observations, lucid de- 

 scriptions and logical deductions, a master- 

 ful zoological treatise such as rarely ap- 

 pears in these days. 



I have arbitrarily chosen the year 1890 

 as a dividing point in the history of pro- 

 tozoology. Before this the work was 

 chiefly descriptive and taxonomic, after 

 this it became more speculative and ex- 

 perimental, although it also developed 

 along the quite unexpected lines of prac- 

 tical biology and public hygiene. For my 

 purpose here I shall not speak of the 

 splendid descriptive work, especially on 

 parasitic forms, that has been done since 

 1890, but will devote my time to a short 

 statement of the activities in certain other 

 lines of protozoology, especially the cyto- 

 logic, pathogenic and general biological. 



I. THE CYTOLOGIC SIDE 



In a strict sense all work on protozoa 

 might be classed as cytological since it has 

 to do with the single cell. But there are 

 two ways of looking at these cells. We 

 may regard them, on the one hand, as 

 morphological units of structure compar- 

 able with the single tissue cell, or, on the- 

 other hand and following Whitman in his 

 interpretation of the egg cell as an organ- 

 ism, we may regard them as complete or- 

 ganisms performing all of the functions of 

 higher animals. Looked at from this 

 point of view the inadequacy of the cell 

 theory as applied to protozoa is obvious. 



In a strictly morphological sense then 

 protozoology includes the study of cell 

 structures homologous with the morpho- 

 logical elements of egg and tissue cells — 

 but these structures are more primitive, 

 more generalized, and, in a sense, more 

 easily correlated with their functions in 

 the cell. 



First, as to the structure of protoplasm. 

 We are generally agreed at present that it 

 is inaccurate to speak of any one structure 

 as common to all protoplasm, but many 

 eytologists, amongst whom Biitschli, work- 

 ing chiefly on protozoa, was the first, be- 



