AND THE HEALING ART 509 



Cattle are liable to tubercle, and, when affected with it, may become a very serious 

 source of infection for human beings, more especially when the disease affects the 

 udders of cows, and so contaminates the milk. By virtue of the close affinity that 

 prevails between the lower animals and ourselves, in disease as well as in health, 

 tuberculin ]:)roduces fever in tubercular cows in doses which do not affect healthy 

 beasts. Thus, by the subcutaneous use of a little of the fluid, tubercle latent in 

 internal organs of an a})parently healthy cow can be with certainty revealed, 

 and the slaughter of the animal after this discovery protects man from infection. 



It has been ascertained that glanders presents a precise analogy with tubercle 

 as regards the effects of its toxic products. If the microbe which has been 

 found to be the cause of this disease is cultivated in appropriate media, it produces 

 a poison which has received the name of mallein, and the subcutaneous injection 

 of a suitable dose of this fluid into a glandered horse causes striking febrile 

 symptoms which do not occur in a healthy animal. Glanders, like tubercle, 

 ma}^ exist in insidious latent forms which there was formerly no possibility of 

 detecting, but which are at once disclosed by this means. If a glandered horse 

 has been accidentally introduced into a large stable, this method of diagnosis 

 surely tells if it has infected others. All receive a little mallein. Those which 

 become affected with fever are slaughtered, and thus not only is the disease 

 prevented from spreading to other horses, but the grooms are protected from 

 a mortal disorder. 



This valuable resource sprang from Koch's work on tuberculin, which has 

 also indirectly done good in other ways. His distinguished pupil, Behring, has 

 expressly attributed to those researches the inspiration of the work which led 

 him and his since famous collaborateur, the Japanese Kitasato, to their surprising 

 discovery of antitoxic serum. They found that if an animal of a species liable 

 to diphtheria or tetanus received a quantity of the respective toxin, so small as 

 to be harmless, and afterwards, at suitable intervals, successively stronger and 

 stronger doses, the creature, in course of time, acquired such a tolerance for the 

 poison as to be able to receive with impunity a (quantity \'ery nuich greater than 

 would at the outset have proved fatal. So far, we have nothing more tlian 

 seems to correspond with the effects of the increasingly })otent cords in Pasteur's 

 treatment of rabies. But what was entirely new in their results was that, if 

 blood was drawn from an animal which had acquired this high degree of artiticial 

 immunity, and some of the clear fluid or serum which exuded from it after it had 

 clotted was introduced under the skin of another animal, this second animal 

 acquired a strong, though more transient, immunit\- against the particular 

 toxin concerned. The serum in some wav counteracted the toxin ov was anti- 

 toxic. But, more than that, if some of the antitoxic serum was applied to an 



