5o8 ON THE INTERDEPENDENCE OF SCIENCE 



the body in a nutrient liquid, with the result that it acquires poisonous qualities 

 of astonishing intensity, comparable to that of the secretion of the poison-glands 

 of the most venomous serpents. And they also ascertained that the liquid 

 retained this property after the microbes had been removed from it by filtration, 

 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 impossible to understand. 

 Thus, in diphtheria 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 lock- 

 jaw. This remains localized 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 nature ; a product of the growth 

 of the tubercle 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 disease, in any of its 

 varied forms, exhibited inflammation in the affected part and general fever 

 after receiving under the skin an amount of the material which had no effect 

 whatever upon healthy persons. I witnessed in Berlin some instance 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 undergone great improvement. By repetitions of such 

 procedures, ulcers which had previously been steadily advancing, in spite of 

 ordinary treatment, became greatly reduced in size, and in some instances 

 apparently cured. Such results led Koch to believe that he had obtained an 

 effectual means of dealing with tubercular disease in all its forms. Unhappily, 

 the apparent 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 was strongly urged to publish before he was himself disposed to 

 do so, and we cannot but regret that he yielded to the pressure put upon him. 



But though Koch's sanguine anticipations were not realized, it would be 

 a great mistake to suppose that his labours with tuberculin have been fruitless. 



