3i6 GREAT MEN OF SCIENCE 



devoted to systematisation, they contain besides a mass of 

 special observations and of ideas going beyond these; and he 

 influenced in a similar way a wide circle of pupils.^ For 

 example, at this very early period he already regarded the 

 smallest living beings as the cause of infectious diseases, for 

 which view he gives a number of pertinent reasons. ^ Par- 

 ticular mention should be made of the fact that Linnaeus, as 

 a result of experience derived from his travels, and extensive 

 breeding experiments on plants under the greatest possible 

 change of conditions, soil, and climate, thoroughly satisfied 

 himself concerning the astonishing invariability of existing 

 species, but that he did not regard this invariability as un- 

 limited. He observed the production of hybrid plants in 

 the botanical gardens, and produced them experimentally; 

 studied fertile and sterile hybrids, and saw in the production 

 of such changed forms of plants a pointer towards a possible 

 understanding of the production of new species in the 

 course of long periods of time.^ Furthermore, he regarded 

 excessively favourable conditions of life as a special cause of 

 the occurrence of new varieties. We see here how unjust it is 

 that Linnaeus' great achievement of having demonstrated 

 the very great and quite general stability of specific form, 

 which is the foundation of all system in the plant and animal 

 world, in later times gradually became almost a reproach to 

 him, as though he had no desire to see any further; indeed, 

 almost as if his personal characteristic had been the defence 

 of complete invariability of species. Surely the fact alone 



^ Much of this is found in Linnaeus' Philosophia Botanica (Stockholm, 

 1 751), and in the work published by Giesecke, Prdlectiones Caroli a 

 Z.j««e' (Hamburg, 1792). 



2 xhe many and varied achievements of Linnaeus are fully appreciated 

 in detail in a work published by the Swedish Academy, Carl von Linnfs 

 Bedeutunf; ah Naturforscher und Arzt, Jena, 1909. See particularly 

 pp. 148 to 188 in Part IV. 



3 'He dared to proclaim plantas hybridas an J gave posterity a sug- 

 gestion oi specierum causaiti,' said Aszelius in a volume published by him 

 in 1823, and containing notes and additions of manuscript jottings by 

 Linnaeus concerning himself. German edition, 1826, p. 83. 



