464 GROWTH OF BIOLOGY IN THE NINETEENTH CENTURY. 



in spite of their small size, yot in viituc of their ineoneeivalile multi- 

 tude, strata many meters thick. The chalk clitis on the coasts of 

 Riigfen and of Enofland arc huilt up of the remains of foraminifera; 

 many islands in the South Sea. of the wonderful siliceous framework 

 of radiolaria. and strata, such as the diatomaceous eai-th of Bilina, of 

 the siliceous shells of diatoms. 



But still more important than these highly interesting' facts for our 

 gen«'ral knowledge of nature was a second series of discoveries which 

 I would place by the side of the cell theory as a sei-ond capital achieve- 

 ment of the century in the (le|)artment of ttioloo-y. Minute organisms 

 are recognized as the cause of widely distriltuted processes of putre- 

 faction, of fermentation, and of very numerous diseases of plants and 

 of animals. They an' unicellular alga-, fungi, l)acteria, and allied 

 micro-organisms. 



Three great investigators have here been the])ioneers — in the botan- 

 ical depai'tment, de Bary, who laid the foundation for the study of 

 diseases of plants by the elaboration of suital)le methods of observa- 

 tion and ])rocesses of cultivation: in the bacteriological department, 

 Pasteui" and Kobert Koch. The great French investigator, equally 

 distinguished as a chemist and as a biologist, and particularly Robert 

 Koch, have by their experimental methods — among which pure cul- 

 tures, artificial nutriment (Xiihrljoden), the gelatin processes, and 

 transfer by inoculation, stand at the head — attorded ways and means 

 which we nuist thank for an immense enrichment of our knowledge. 



Again, in the short span of two or three decades, an extensive depart- 

 ment of science has been established — I mean bacteriology. For it is 

 the characteristic phenomenon of our age, with its greatly increased 

 interest in science, with its more perfect organization of expert work 

 (gelchsten arbeit), with its numerous scientific institutions, with its 

 enlightened and accelerated intercommunication of ideas by journals 

 and !)}• the daily press, that if a new mark is set up, and if the wa}- to 

 its attainment^ — the scientific method — is found, then everywhere the 

 forces of work are roused to feverish activity as in no earlier time. 

 How quickly were the first abortive experiments followed by a knowl- 

 edge of microbes. The exciting agents of anthrax, of septicemia and 

 pyemia, of erysipelas, of typhus, of intermittent fever and of cholera, 

 of tuberculosis, of malaria, and of many other infectious diseases of 

 men and of animals, down to insects and worms, were discovered, and 

 their life histories studied. 



It is a grand thing to enrich our stock of knowledge by new dis- 

 coveries; yet it may be not less important and serviceable to refute 

 and eliminate errors, and especially the errors which infest science 

 itself. The less men knew in the past of the vital process the more 

 ready they were to accept as an established fact the hypothesis of spon- 

 taneous generation (Urzeugung) — that is to say, the assumption that 



