4 INTRODUCTION 



was thus given to the generalization, but the possibility that the 

 rods might be the consequence and not the cause of anthrax 

 was not excluded, and further experiments of more elaborate 

 and painstaking nature became necessary. By well-known 

 methods, "pure cultures" were made of the rod -shaped 

 microbes, i.e. they were grown in an artificially -prepared 

 medium, free from all other germs, in such a way that such 

 other germs continued to be excluded. Healthy animals were 

 then inoculated from these pure cultures, with the result that 

 typical anthrax at once manifested itself. In this way the 

 original generalization was experimentally verified. By similar 

 methods of procedure many other dise'ases have been proved 

 to be due to the noxious action of specific microbes. Other 

 instances of the experimental method will be given in the course 

 of this work. 



In all such cases the value of the imagination can hardly 

 be overestimated. To frame a reasonable generalization from 

 a mere collection of facts requires a mental jump, so to speak, 

 and the man of real genius in the scientific world the " epoch- 

 making " man is he who can make such leaps in the dark 

 with the best prospect of alighting on solid ground. 



THE STUDY OF ANIMALS 







SUBJECT-MATTER OF BIOLOGY. All material objects are com- 

 posed of what is known as "matter", about which all that can 

 positively be stated is that it occupies space, takes up room, as 

 we may say. Matter is liable to undergo change, and these 

 changes are dealt with by chemistry and physics; by the former 

 if they involve modification in composition; by the latter if they 

 do not. One particular kind of matter is distinguished by the 

 possession of life, which is recognized by its effects, though we 

 are profoundly ignorant of its real nature. Biology \ the science 

 of life (Greek bios, life; logos, a discourse), deals with living 

 matter, that is to say, with plants and animals, from all possible 

 points of view. As organisms are constantly undergoing both 

 chemical and physical changes, it is obvious that a knowledge 

 of physics and chemistry is, to say the least, of immense value 

 to the biologist. It has even been suggested that life will some 

 day be explained by chemical and physical laws; but, even if 



