Decembee 31, 1920] 



SCIENCE 



617 



minor imperfections in this fundamental work 

 on artificial immunity. For example, it 

 worild now appear that the so-called attenu- 

 ated cultures of the bacillus of fowl cholera, 

 used for purposes of immunization, were not 

 so much attenuated as actually dead, and that 

 the material inoculated consisted of a mixture 

 of dead bacilli and their metabolic and dis- 

 integrative products. In other words, it 

 seems that Pasteur without perceiving it had 

 discovered not only a principle of wide appli- 

 cability in inducing artificial immunity, but 

 a general method of utilizing dead bacteria as 

 vaccines, and one which in more recent times 

 has been widely resorted to in preventing out- 

 breaks of typhoid fever, cholera, and some 

 other diseases. 



In 1882 antirabic inoculation was perfected. 

 Pasteur had, of course, reflected deeply on the 

 som-ces of the immune state and in explana- 

 tion of it he inclined to the view that the 

 basis of the phenomenon was a nutritive con- 

 dition. He conceived that in the course of 

 that form of microbic development within the 

 / body which came to a spontaneous end and 

 left the individual protected, certain essential 

 foodstuffs were consumed, in virtue of which 

 the same variety of microbe could not later 

 gain another foothold. Time has not upheld 

 this simple conception; but when it was 

 formulated the subject matter of bacteriology 

 was still too fragmentary and scanty to point 

 to the deeper underlying chemical and bio- 

 logical processes involved. Indeed, nearly ten 

 years elapsed until Behring's discovery of 

 antitoxic immunity brought about a revolu- 

 tion in the prevailing ideas and opened up 

 new and fascinating vistas of research. 



We have now reached the period at which 

 the German school of bacteriology, led by 

 Eobert Koch, has arisen beside the French. 

 Koch's career in science was meteoric. From 

 an inconspicuous country practitioner he be- 

 came, in the period beginning about 1880, the 

 outstanding world figure in bacteriology. 

 But his greatest work was completed in rela- 

 tively few years, although that of his pupils 

 has continued up to and is still potent at the 

 present day. It is informing to reflect that 



just as Davaine made the first signal advance 

 in the experimental inoculation of disease 

 with the anthrax bacillus, and Pasteur the 

 first dramatic demonstration of the practic- 

 ability of protective inoculation with bac- 

 terial cultures also with that bacillus, Koch 

 rose into fame through the study of its life 

 history by direct observation imder the micro- 

 scope. But Koch's greater contribution to 

 bacteriology consisted of a method of cultiva- 

 tion so perfected that pure growths of bac- 

 terial species were readily obtainable. The 

 consequence was that in a very brief period 

 of years a whole host of pathogenic bacteria 

 or incitants of diseases of man and animals 

 was secured, among which were the highly im- 

 portant bacilli of tuberculosis, cholera, typhoid 

 fever, diphtheria, tetanus, dysentery, plague, 

 meningitis and many others. 



Up to the period we are now considering, 

 all the diseases of microbic origin thus far in- 

 vestigated successfully belonged to the class 

 in which the bacteria invaded the blood and 

 the internal organs. But now w^ are about to 

 learn of another kind of disease induced by a 

 class of bacteria which are peculiar in that 

 they do not migrate throughout the body but 

 remain fixed in a special tissue or part, where 

 they multiply and secrete a poison which finds 

 its way first into the lymph, then into the 

 blood and the organs generally. This latter 

 class of microbes produces its effects to which 

 we give the name of disease, and of which 

 diphtheria and tetanus are examples, through 

 the operation of a poison, peculiar to each, 

 and in each instance attacking by preference 

 certain definite organs or parts of them. Thus 

 the poison elaborated by the diphtheria bacil- 

 lus selects especially the lymphatic organs, 

 heart and nervous system for its action, and 

 the tetanic poison the nerve cells governing 

 muscular contraction. 



We have now returned by a route somewhat 

 circuitous perhaps to the point from which 

 we started, namely diphtheria and its antidote. 

 But in the course of the journey we have 

 taken, new points of view have been gained 

 which, as will appear, are to transform en- 



