THE RECENT DEVELOPMENT OF BIOLOGY 



BY JACQUES LOEB 



[Jacques Loeb, Professor of Physiology, University of California, since 1902. b. 

 Germany, April 7, 1859. Graduate of the Ascanisches Gymnasium, Berlin. 

 Studied medicine, Berlin, Munich; M.D. Strassburg. Assistant in Physiology, 

 University of Wiirzburg, 1886-88 ; ibid., University of Strassburg, 1888-90 ; 

 Biological Station, Naples, 1889-91 ; Associate in Biology, Bryn Mawr, 1891-92; 

 Assistant Professor of Physiology and Experimental Biology, University of 

 Chicago, 1892-95; Associate Professor, ibid., 1895-1900;' Professor, ibid., 

 1900-02. Author of The Heliotropism of Animals and its Identity with the 

 Heliotropism of Plants; Physiological Morphology; Comparative Physiology of the 

 Brain and Comparative Psychology; Studies in General Physiology; The Dynamics 

 of Living Matter.} 



THE task allotted to me on this occasion is a review of the develop- 

 ment of biology during the last century. The limited time at our 

 disposal will necessitate many omissions and will force me to confine 

 myself to the discussion of a few of the departures in biology which 

 have led or promise to lead to fertile discoveries. 



The problem of a scientific investigator can always be reduced to 

 two tasks; the first, to determine the independent variables of the 

 phenomena which he has under investigation, and secondly, to find 

 the formula which allows him to calculate the value of the function 

 for every value of the variable. In physics and chemistry the inde- 

 pendent variables are in many cases so evident that the investiga- 

 tion may begin directly with the quantitative determination of the 

 relation between the change of the essential variable and the func- 

 tion. In biology, however, the variables, as a rule, cannot be recog- 

 nized so easily, and a great part of the mental energy of the investi- 

 gators must be spent in the search for these variables. To give an 

 example, we know that in many eggs the development only begins 

 after the entrance of a spermatozoon into the egg. The spermatozoon 

 must produce some kind of a change in the egg, which is responsible 

 for the development. But we do not know which variable in the 

 egg is changed by the spermatozoon, whether the latter produces a 

 chemical or an osmotic change, or whether it brings about a change 

 of phase or some other effect. It goes without saying that a theory 

 of sexual fertilization is impossible until the independent variable 

 in the process of sexual fertilization is known. 



The investigations of the biologist differ from those of the 

 chemist and physicist in that the biologist deals with the analysis 

 of the mechanism of a special class of machines. Living organisms 



