August 4, 1911] 



SCIENCE 



135 



have been made; culture methods have 

 been extended to the spirochtetes and some 

 good observations have been made on the 

 interrelationships of parasitic flagellates 

 and hffimosporidia. In my opinion, how- 

 ever, this branch of protozoology has seen 

 its period of greatest development and, 

 save for the working out of life histories, 

 the protozoologist may well turn over the 

 pathogenic protozoa to the departments of 

 medicine, public hygiene and public sani- 

 tation. 



In preparing this lecture I was tempted 

 to dwell longer on this interesting and im- 

 portant phase of protozoology and to give 

 a detailed account of the trials and diffi- 

 culties experienced in establishing the 

 causes of protozoan diseases. Also I 

 should like to speak at length on the prob- 

 able causes of smallpox, scarlet fever, 

 rabies, trachoma and molluscum contag- 

 iosum, and about the many fruitless at- 

 tempts to trace human cancer to protozoa, 

 but I must hasten on to a third, and, as I 

 believe, the most important, branch of 

 protozoology, general biology. 



in. THE BIOLOGICAL SIDE 



Here the field of protozoology expands 

 so widely that I can speak of only a few 

 topics, for the problems are fundamental 

 and universal and merge into those which 

 every biologist is striving to solve. 



Verworn in 1888 made the statement 

 that protozoa seem to have been especially 

 adapted by nature for the purposes of the 

 physiologist, for here, in the single cell, are 

 performed all of the functions which 

 higher animals perform. This was twenty- 

 three years ago and the fact that strikes 

 us to-day is that, in spite of the vast 

 amount of work done in the subject, these 

 same fundamental vital activities remain 

 almost as obscure as they were then. 

 Some progress, nevertheless, has been 



made. The early experiments of Balbiani, 

 Verworn, Gruber, Hofer and a score of 

 others demonstrated that enucleate frag- 

 ments of cells could not secrete, 'grow nor 

 continue to live, while Verworn in 1891 

 showed that the isolated nucleus is equally 

 impotent. The axiom was thus laid down 

 that nucleus and cytoplasm are equally 

 important for the proper performance of 

 vital activities. 



At this earlier period it was thought 

 that great light would be thrown upon the 

 vital functions of higher animals through 

 study of the simpler activities in protozoa, 

 especially in the directions of (1) diges- 

 tion and assimilation, (2) irritability, 

 (3) growth and reproduction, (4) regen- 

 eration, (5) sex and fertilization, (6) 

 death and physical immortality, etc., 

 but it was soon discovered that under the 

 mask of simplicity lie hidden the same 

 great problems which puzzle biologists in 

 every other field of study. Let me illus- 

 trate briefly some of these points. 



1. Digestion and Assimilation. — The 

 early observations by Le Dantec, Meissner, 

 Fabre-Domergue, Greenwood and others 

 from 1888-1894 demonstrated the presence 

 of some mineral acid in connection with 

 proteid digestion in different types of 

 protozoa, and it was suggested that some 

 simple ferment, acting in an acid medium, 

 is responsible for digestion in these single 

 cells. This suggestion was confirmed by 

 Hartog and Dixon in 1901, who isolated a 

 proteolytic ferment active in an acid 

 medium; but the subject became more 

 complicated when Mouton and Mesnil in 

 1902-03 isolated a proteolytic ferment that 

 was active in an alkaline medium, and 

 suggested that the digestive ferment in 

 protozoa is more like trypsin than pepsin. 

 Finally, Nierenstein and Metalnikoff, in 

 1903-07 showed that both types of fer- 

 ment are involved, digestion beginning with 



