GEOWTH OF BIOLOGY m THE NINETEENTH CENTUEY. 471 



sion upon the market, produce in stronger and in weaker doses before 

 he studies their application as medicines for this or that diseased con- 

 dition of man. 



Our materia medica has been greatly enriched in this way during 

 the last half century, and the increase goes on yearly. T will liere 

 call to mind the new processes of cure first tested"upon animals which 

 are acquisitions of the latest dates: Koch\s tul)erculin, the diphtheria 

 serum of Behring and Ehrlich, and the other different kinds of serum 

 that have been proposed against lockjaw. th(> plague, and many dis- 

 eases of animals, as well as Pasteur's peculiar nicthod of treatment of 

 hydrophobia. 



In the second direction I mentioned I have in mind the study of 

 that great host of maladies evoked by the invasion into the animal 

 system of alien parasitic organisms as excitants of disease. Experi- 

 ments upon animals have alone rendered possible that great triumphal 

 march which the biological research of our century has traveled over, 

 discovery treading on the heels of discovery. In order to acquaint 

 themselves with the essence of the trichina disease, Leuckart and 

 Virchow caused trichinous meat to be consumed by man}^ animals 

 selected for experiment, and in that way gained a knowledge of the 

 history of development of the trichina and the mode in which, by its 

 introduction into the body of the infected animal, it produces the 

 different stages of the process of disease. Davaine and Koch cleared 

 up the nature of anthrax by inoculating a healthy, susceptible animal 

 with a tiny drop of blood from an animal suffering from anthrax, and 

 in this simple way infected it so as to establish the development of 

 the anthrax bacillus in all stages. The investigator pursues the same 

 method in all cases, with erysipelas and septicemia, typhus, cholera, 

 the plague, tuberculosis, malaria, and, in a word, all the infectioas 

 diseases which are produced by the lowest fungi, bacteria, sporozoa, 

 and other kinds of parasites. 



But the modern physiologist contemplates with yet greater pride 

 than that which the results of those animal experiments awaken, the 

 extraordinarj^ success which his science has achieved in our century in 

 two other great fields, those of biochemistry and biophysics. 



Under the rule of the vitalistic doctrine the scientific doctrine rife 

 at the beginning of our century was that the organic sul)stances of 

 which the bodies of plants and' animals arc built could only be pro- 

 duced by the peculiar vital forces of these organisms, so that destiny 

 refused to the chemist the power of imitating any such substances by 

 his insuflicient methods. 



One brilliant discovery by Wohler at length shattered the vitalistic 

 error, for he succeeded in producing artificially in his laboratory one 

 of the peculiar products of the vital process of animals, namely, urea. 

 Soon, in the rapid progress upon Avhich organic chemistry now entered, 



