IOWA ACADEMY OF SCIENCES. 77 



inherited disease, was too strongly intrenched in the minds of physicians and peo- 

 ple generally. But Koch brought such conclusive evidence in his first paper that 

 the contagious nature of the disease could not be doubted and is now almost 

 universally accepted. Physicians to-day use the methods proposed by Koch, 

 Ziehl, Ehrlich and others for determining the presence of tubercle bacilli in 

 sputum, lupus and other forms of the disease. A subject that was widely com- 

 mented upon a few years ago in the press of the whole civilized world was the 

 discovery of a toxic product, tuberculin in cultures of tubercle bacillus. This 

 product discovered by Koch is soluble in glycerine. It is a powerful therapeutical 

 agent. In very minute doses, when injected subcutaneously into tuberculous 

 animals, it produces febrile and other decided symptoms. Dr. Sternberg'''' says: 

 " Thi^ discovery must rank as one of tbe first importance in scientific medicine 

 whatever the final verdict may be as to its therapeutic value in tubercular diseases 

 in man." Numerous experiments have been made to determine its value as an 

 agent in diagnosis of tuberculosis in bovine animals. These investigations have 

 not only been carried on in Europe, but in our own country Dr. Pearson^^ has 

 shown how valuable it is in cases of this kind. I may also refer to the value of 

 another product, mallein, which Dr. Theobold Smith*^ and others have used with 

 great success in diagnosis of glanders. 



These and other results which have been obtained along the lines of bacteriology 

 have been of inestimable value to the world at large. We cannot overlook the 

 great work of Pasteur in affording immunity to persons bitten by mad dogs. 

 Hydrophobia, that strange malady which has baffled medical skill will, it is to be 

 hoped, be held in check by the work of this savant. 



Although the cause of this strange and fatal disease is still a mystery, the bene- 

 fits resulting from a series of innoculations are beyond dispute. 



SUSCEPTIBILXTY AND IMMUNITY. 



We can now discuss briefly susceptfbility and immunity. No question in gen- 

 eral medicine and biology is more interesting than those which relate to suscepti- 

 bility and immunity from disease in plants and animals. Certain animals and 

 plants are much more subject to some diseases than others. Tuberculosis is com- 

 mon to man, bovine animals, apes and small herbivorous animals. Anthrax is 

 most common in cattle and sheep; it may be communicated to man, guinea pigs, 

 rabbits and mice. Rats, dogs, and birds are generally exempt. Glanders is 

 most common in equine animals, occasionally forms a loathsome disease in man, 

 but mice, rabbits and cattle are generally exempt. But this difference of a disease 

 is not confined to different species; it often occurs in different individuals of the same 

 species. Thus hog cholera of the U. S. Department of Agriculture^" nearly always 

 takes away a majority of the animals, but a few will not take the disease. 



A case has come under my observation in which various pathogenic germs were 

 innoculated into a rabbit, but all without avail. Again common laboratory expe- 

 rience shows that very young animals are much more liable to resist diseases than 



Weitere Mittheilungen ueber das Tuberkulin, Deutsche Med. Wochenschrift, 1891, 

 No. 43. 



50 Manual of Bacteriology, p. 387. 



MBull. No. 21, Pennsylvania Agrl. Experiment Station. E. P. Niles, Tuberculosis 

 and the Koch test, Virginia Agrl. Exp. Station, vol. II, N. S. No. 3. 



55 W. B. Niles, Bull. No. 20. p. 729, Iowa Agrl. E.vp. Station. 



56Hog Cholera: Its history, nature and treatment, as determined by the inquiries 

 and investigations of the Bureau of Animal Industry, pp. 199. with 16 plates. Govern- 

 ment Printing office, Washington, D. C. See p. 34. 



