9 z THE POPULAR SCIENCE MONTHLY. 



taining a memoir by Dr. Koch on splenic fever (Milzbrand, Charbon, 

 malignant pustule), which seemed to me to mark an epoch in the his- 

 tory of this formidable disease. With admirable patience, skill, and 

 penetration, Koch followed up the life-history of bacillus anthracis, 

 the contasrium of this fever. At the time here referred to he was a 

 young physician, holding a small appointment in the neighborhood of 

 Breslau, and it was easy to predict, as I predicted at the time, that he 

 would soon find himself in a higher position. When I next heard of 

 him he was head of the Imperial Sanitary Institute of Berlin. Koch's 

 recent history is pretty well known in England, while his appreciation 

 by the German Government is shown by the rewards and honors lately 

 conferred upon him. 



Koch was not the discoverer of the parasite of splenic fever. Da- 

 vaine and Rayer, in 1850, had observed the little microscopic rods in 

 the blood of animals which had died of splenic fever. But they were 

 quite unconscious of the significance of their observation, and for 

 thirteen years, as M. Radot informs us, strangely let the matter drop. 

 In 1863 Davaine's attention was again directed to the subject by the 

 researches of Pasteur, and he then pronounced the parasite to be the 

 cause of the fever. He was opposed by some of his fellow-country- 

 men ; long discussions followed, and a second period of thirteen years, 

 ending with the publication of Koch's paper, elapsed, before M. Pas- 

 teur took up the question. I always, indeed, assumed that from the 

 paper of the learned German came the impulse toward a line of in- 

 quiry in which M. Pasteur has achieved such splendid results. Things 

 presenting themselves thus to my mind, M. Radot will, I trust, forgive 

 me if say that it was with very great regret that I perused the dis- 

 paraging references to Dr. Koch which occur in the chapter on splenic 

 fever. 



After Koch's investigation, no doubt could be entertained of the 

 parasitic origin of this disease. It completely cleared up the perplexity 

 previously existing as to the two forms the one fugitive, the other 

 permanent in which the contagion presented itself. I may say that 

 it was on the conversion of the permanent hardy form into the fugitive 

 and sensitive one, in the case of bacillus subtilis and other organisms, 

 that the method of sterilizing by " discontinuous heating " introduced 

 by me in February, 1877, was founded. The difference between an 

 organism and its spores, in point of durability, had not escaped the 

 penetration of Pasteur. This difference Koch showed to be of para- 

 mount inportance in splenic fever. He, moreover, proved that while 

 mice and Guinea-pigs were infallibly killed by the parasite, birds were 

 able to defy it. 



And here we come upon what may be called a band-specimen of 

 the genius of Pasteur, which strikingly illustrates its quality. Why 

 should birds enjoy the immunity established by the experiments of 

 Koch ? Here is the answer. The temperature which prohibits the 



