158 THERAPEUTICS AND PHARMACOLOGY 



the human system is of the greatest importance. Just a year previous 

 to the beginning of the nineteenth century the urea which appears 

 in well-formed crystals in the human organism was discovered by 

 Fourcroy and Vauquelin. This fact, certainly, did not appear so 

 strange, since crystalline matters had already been obtained from 

 plants, but even in the beginning of the century the idea was still 

 firmly rooted in the mind of the naturalist that these substances 

 could only appear as the products of vital energy. This presented 

 itself to the minds of men of that time as an entirely distinct force, 

 which, independent of physical and chemical laws, manifested itself 

 in a characteristic form in the organism. There is no discovery 

 which has so often been quoted in the interest of the medical and 

 other biological sciences as the observations of the chemist Wohler 

 who, in 1828, observed the formation of urea in a substance obtained 

 outside of the system, namely, ammonium cyanide, by the trans- 

 position of atoms. But if we rightly consider this grand discovery, 

 which completely refuted the followers of the theory of vital energy, 

 it would still, perhaps, be possible, in spite of this discovery, to 

 undertake the defense of the theory of vital energy as something 

 beyond the laws of natural science, for neither Wohler's synthesis 

 nor the manner of formation of urea from carbonyl chloride and 

 ammonia, or from ethyl carbonate and ammonia, or from cyanamide 

 by hydration, or from ammonium carbonate, as well as from leucine 

 and from other substances of the organism, gives any actual expl.ana- 

 tion of the formation of urea in the system. The synthetic product 

 is identical with the product of the organism, but the synthesis, 

 or rather the formation of urea in the body takes place in accord- 

 ance with laws, the exact nature of which we do not fully know even 

 at the present day. This is, indeed, the case with a large number of 

 other substances derived from animals or plants. Although the 

 chemical constitution of substances was constantly more and more 

 exactly defined in the course of the nineteenth century, the manner 

 of formation in the organism still remains hidden from us. We 

 frequently find it stated that we must not simply compare the pro- 

 cesses of the organism to the test-tube experiment of the chemist. 

 There is no doubt that processes of metabolism take place within the 

 body for which the synthesis performed outside of the organism 

 gives no explanation. From my somewhat dissentient attitude in 

 regard to the conclusions drawn from Wohler's experiment, I might 

 for a moment be thought to favor the view that the activity of the 

 organism in the form of vital energy is beyond the laws of natural 

 science, but that is not the case. Even if in synthetic experiments 

 other means are employed than are available within the organism, 

 the supposition is justified by the possibility of synthesis, that the 

 organic processes occur in accordance with purely physical and 



