GEOWTH OF BIOLOGY IN THE NINETEENTH CENTURY. 473 



velocity of nervous transmission might be investigated. The ophthal- 

 moscope of Helmholtz and the laiyjig-oscope of Czemiak (Mia))Ied the 

 investigator to aid practical medicine by giant strides into the view of 

 the interior of two important organs. 



The improvement of the instrumental equipment of physiology has 

 continued without cessation to the end of the century. Every new 

 ac(iuisition of physics is immediately made available to physiology 

 and medicine. Thus the physician is already, inmiediately after ROnt- 

 gen\s epoch-making discovery, in condition to ])ring into clear view 

 upon the photograj^ihic plate, by suitable application of the so-called 

 X-rays, parts hidden in the depths of the human body and absolutely 

 invisible to the eye, such as single sections of the skeleton. 



So pioneer investigations of physiologists trained in physics — a 

 Helmholtz and a Du Bois-Reymond, a Fechner, Weber, Ludwig, 

 Briicke, and Pfliiger — as upon another occasion I have in a few Avords 

 summarily remarked, have in our century '"created a special physics 

 of the nerves and muscles, a physics of the organs of sense, a 

 mechanics of the skeleton and organs of locomotion, a mechanics of 

 respiration and circulation." 



"The eye was explained as a camera obscura arranged according to 

 the laws of optics; the ear as a physical apparatus arranged to bring 

 the nerves to the perception of acoustic vibrations by means of suit- 

 able organic structures, vibrating membranes and rods, which, like 

 the wires of a pianoforte, are tuned to the different notes. The larjnix 

 became«a reed pipe, adapted to the production of tones in vibrations, 

 the lungs serving as the bellows. The laws of filtration and osmosis 

 were adduced for the explanation of absorption and secretion. By a 

 composition of intricate apparatus called a calorimeter the physiologist 

 now determined the amount of heat reckoned in calories produced in 

 the course of a day by an animal body, and undertook the difficult task 

 of striking a balance sheet of the animal transformation of energy, the 

 animal body being debtor to nutriment of different kinds in so many 

 calories of energy, while upon the credit side were suiuiiicd up the 

 amounts of energy which the body had given in the form of iicat pro- 

 duced or mechanical work, and which are alisorbcd in the processes of 

 metal )olisjn." 



In the face of the great triumi^hs which physiological science cele- 

 brated by the introduction of chemical and physical nietliods. the 

 majority of investigators became accustomed to the view, to which 

 they were led, too, by the brilliant exposition of it by Du Bois-Rey- 

 mond, that physiology, imagined as complete, is nothing else than bio- 

 physics and biochemistry, and that it has no just pretension to rank as 

 a true science, except so far as it is an application of chemistry and 

 physics, d3mamics and mathematics. 



From the extreme of a '-shallow vitalism," a^ Du Bois-Reymond 

 called it, physiologists mostly went to the opposite extreme of a deso- 



