26 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



drate bodies has been determined, and bodies belonging to this group have 

 been synthetically constructed in the laboratory. Moreover, the work of 

 Schiitzenberger and of Grimaux gives promise that before long, proteid bodies 

 may be produced by similar methods. Physiologists have shown, furthermore, 

 that the digestion which takes place in the stomach or intestine may be effected 

 also in test-tubes, and at the present day probably no one doubts that in the 

 act of digestion we have to deal only with a series of chemical reactions which 

 in time will be understood as clearly as it is possible to comprehend any form 

 of chemical activity. Indeed, the whole history of food in the body follows 

 strictly the great mechanical laws of the conservation of matter and of energy 

 which prevail outside the body. No one disputes the proposition that the 

 material of growth and of excretion comes entirely from the food. It has 

 been demonstrated with scientific exactness that the measurable energy given 

 off from the body is all contained potentially within the food that is eaten, 1 

 and may be liberated outside the body by ordinary combustion. Living 

 things, so far as can be determined, can only transform matter and energy ; 

 they cannot create or destroy them, and in this respect they are like inanimate 

 objects. But, in spite of the triumphs which have followed the use of the 

 experimental method in physiology, every one recognizes that our knowledge 

 is as yet very incomplete. Many important manifestations of life cannot be 

 explained by reference to any of the known facts or laws of physics and 

 chemistry, and in some cases these phenomena are seemingly removed from 

 the field of experimental investigations. As long as there is this residuum 

 of mystery connected with any of the processes of life, it is but natural that 

 there should be two points of view. Most physiologists believe that a& 

 our knowledge and skill increase these mysteries will be explained, or rather 

 will be referred to the same great final mysteries of the action of matter and 

 energy under definite laws, under which we now classify the phenomena of 

 lifeless matter. Others, however, find the difficulties too great, they perceive 

 that the laws of physics and chemistry are not completely adequate at present 

 to explain all the phenomena of life, and assume that they never will be. 

 They suppose that there is something in activity in living matter which i& 

 not present in dead matter, and which for want of a better term may be desig- 

 nated as vital force or vital energy. However this may be, it seems evident 

 that a doctrine of this kind stifles inquiry. Nothing is more certain than the 

 fact that the great advances made in physiology during the last four decades 

 are mainly owing to the abandonment of this idea of an unknown vital force 

 and the determination on the part' of experimenters to push mechanical 

 explanations to their farthest limit. There is no reason to-day to suppose that 

 we have exhausted the results to be obtained by the application of the methods 

 of physics and chemistry to the study of living things, and as a matter of 

 fact the great bulk of physiological research is proceeding along these lines. It 

 is interesting, however, to stop for a moment to examine briefly some of the 

 problems which as yet have escaped satisfactory solution by these methods. 

 1 Kubner : Zeitschrift fur Biologic, Bd. xxx. S. 73, 1894. 



