424 



SCIENCE. 



[N. S. Vol. IV. No. 91. 



While the intensity of rabies in the rab- 

 bit is undoubtedly due to a peculiarly viru- 

 lent form of the microbe concerned, we 

 cannot suppose that the daily diminishing 

 potency of the cord suspended in dry warm 

 air is an instance of attenuation of virus, 

 using the term ' virus ' as synonymous with 

 the microbe concerned. In other words, 

 we have no reason to believe that the 

 special micro-organism of hydrophobia con- 

 tinues to develop in the dead cord and 

 produce successively a milder and milder 

 progeny, since rabies cannot be cultivated 

 in the nervous system of a dead animal. 

 We must rather conclude that there must 

 be some chemical poison present which grad- 

 ually loses its potency as time passes. And 

 this leads me to refer to another most im- 

 portant branch of this large subject of bac- 

 teriology, that of the poisonous products of 

 microbes. 



It was shown several years ago by Koux 

 and Yersin, working in the Institut Pas- 

 teur, that the crust or false membrane which 

 forms upon the throats of patients aflfected 

 with diptheria contains bacteria which can 

 be cultivated outside the body in a nutrient 

 liquid, with the result that it acquires poi- 

 sonous qualities of astonishing intensity, 

 comparable to that of the secretion of the 

 poison glands of the most venomous ser- 

 pents. And they also ascertained that the 

 liquid retained this property after the mi- 

 crobes had been removed from it by filtra- 

 tion, which proved that the poison must be 

 a chemical substance in solution, as dis- 

 tinguished from the living element which 

 had produced it. These poisonous products 

 of bacteria, or toxins, as they have been 

 termed, explain the deadly effects of some 

 microbes, which it would otherwise be im- 

 possible to understand. Thus, in diptheria 

 itself the special bacillus which was shown 

 by Loffler to be its cause does not become 

 propagated in the blood, like the microbe 

 of chicken cholera, but remains confined to 



the surface on which it first appeared ; but 

 the toxin which it secretes is absorbed from 

 that surface into the blood, and so poisons 

 the system. Similar observations have been 

 made with regard to the microbes of some 

 other diseases, as, for example, the bacillus 

 of tetanus or lockjaw. This remains local- 

 ized in the wound, but forms a special toxin 

 of extreme potency, which becomes absorbed 

 and diffused through the body. 



Wonderful as it seems, each poisonous 

 microbe appears to form its own peculiar 

 toxin. Koch's tuberculin was of this na- 

 ture, a product of the growth of the tuber- 

 cle bacillus in culture media. Here, again, 

 great effects were produced by extremely 

 minute quantities of the substance, but 

 here a new peculiarity showed itself, viz., 

 that patients affected with tubercular dis- 

 ease, in any of its varied forms, exhibited 

 inflammation in the affected part and gen- 

 eral fever after receiving under the skin an 

 amount of the material which had no effect 

 whatever upon healthy persons. I wit- 

 nessed, in Berlin, some instances of these 

 effects, which were simply astounding. 

 Patients affected with a peculiar form of 

 obstinate ulcer of the face showed, after a 

 single injection of the tuberculin, violent 

 inflammatory redness and swelling of the 

 sore and surrounding skin; and, what was 

 equally surprising, when this disturbance 

 subsided the disease was found to have un- 

 dergone great improvement. By repeti- 

 tions of such procedures, ulcers which had 

 previously been steadily advancing, in spite 

 of ordinary treatment, became greatly re- 

 duced in size, and in some instances appar- 

 ently cured. Such results led Koch to be- 

 lieve that he had obtained an effectual 

 means of dealing with tubercular disease 

 in all its forms. Unhappily, the appar- 

 ent cure proved to be only of transient 

 duration, and the high hopes which had 

 been inspired by Koch's great reputation 

 were dashed. It is but fair to say that he 



