QUANTITATIVE METHOD AND PRIMORDIA 49 



ment of certain vital functions several parts of physiology have 

 reached a degree of accuracy hardly inferior to the exactitude 

 prevalent in physical and chemical sciences. I content myself 

 with a few examples. 



The measurement of the so-called personal equation and of 

 the duration of a sensation produced by a luminous impression 

 upon our eye (JOSEF PLATEAU) have been the origin of the 

 modem physiology of the nervous system and the sense organs, 

 which includes experimental psychology. In this part of 

 biological science a new world of facts and phenomena has been 

 disclosed by means of measurement. The relations between 

 stimuli and the physiological reactions which they produce, 

 the physiology and the optical contrivances of the human eye, 

 belong to the most admirable conquests of modern science. 

 Here INVESTIGATION IS MEASUREMENT and ahnost 

 every conclusion is drawn from a comparison of figures. 

 Similarly the quantitative method has been introduced in 

 physiology by the application of physics and chemistry to the 

 study of physiological functions. Our knowledge of aerobic 

 and anaerobic respiration, the conception of respiration in 

 general, our knowledge of the osmotic properties of cell-sap 

 (DE VRIES) and other liquids contained in the body of living 

 beings (HAMBURGER) have been built up by means of 

 methods borrowed from physics and chemistry, which are 

 themselves governed by the quantitative method. 



DARWIN'S remarkable experimental investigation of self- 

 and cross-fertilization is based upon the measurement of the 

 dimensions and the fertility of self- and cross-fertilized speci- 

 mens. This line of experimental research is in close relation 

 with the study of heredity. It is full of promise, although it is 

 for the time being somewhat overlooked. 



In the present state of biological science there is a rather 

 disconcerting discordance between physiology, which is the 

 investigation of the functions of the living beings, and descrip- 

 tive biology, which is the study of the living objects themselves. 

 In physiology quantitative investigation is already prepon- 

 derant. In anatomy, morphology, embryology and in the 

 description of species we still follow almost entirely the quali- 

 tative method. Physiology would say, for instance, that a 

 certain thing a is 1-13 times as long as h ; descriptive biology 

 would say that a is rather longer than h. On the one hand an 

 exact description is used ; on the other hand, vague terms. 



§ 41a. — Among the students of descriptive biology a pre- 

 judicial misconception seems to prevail. Many of them seem 

 to believe that the use of the quantitative method is very easy 

 and simple when applied to physics, chemistry and physiology. 



