164 Professor Tyndall [Jan. 16, 



Zoologie ' a memoir on a disorder called by the French charhon. by the 

 Germans Milzhrand, and by tlie English, woolsorters' disease, malig- 

 nant pustule, or S2)lenic fever. This memoir seemed to me to mark 

 an epoch in the history of a most deadly malady, and also in the 

 history of the germ theory itself. The coutagium of splenic fever is 

 an organism which apj^ears as rods in the blood and tissues of men 

 and auimals smitten by the fever. The name of the organism is 

 Bacillus anthracis, and with consummate skill, patience, and penetra- 

 tion, in the memoir referred to, its life-history was completely 

 followed out. It was easy to predict that the author of the paper, 

 who at that time held a small appointment in the neighbourhood of 

 Breslau, would soon find himself transferred to a hioher postion. 

 The admirable worker to wliom I here refer was Dr. Koch, and the 

 next time I heard of him he was head of the Imperial Sanitary 

 Institute of Berlin. 



Koch was not the discoverer of the parasite of sjDlen^'c fever. As 

 early as 1850, Davaine and Eeyer had observed the microscopic rods 

 in the blood of animals that had died of the disease. But they were 

 at the time unconscious of the significance of their observation, and 

 for thirteen years allowed the matter to drop. Eoused by the 

 researches of Pasteur, Davaine returned to the subject in 1863, and 

 then affirmed the rods to be the contagium of the fever. He was 

 opposed by some of his own countrymen, and hot discussions on the 

 subject were carried on in the Academy of Sciences and elsewhere. 

 PoUender, Brauell, and Burden Sanderson made important contribu- 

 tions to the etiology of the disease; but knowledge was contradictory, 

 uncertain, and incomplete till Koch grasped the subject in 1876, 

 and, with the ardour of a youth and the caution of a veteran in 

 microscopic research, cultivated the organism, reconciled contradic- 

 ti(ms, and placed beyond the possibility of doubt the parasitic 

 character of splenic fever. This result again was achieved by the 

 only means open to the investigator ; namely, by the inoculation of 

 healthy animals with a living virus derived either from artificial 

 cultivations or from other animals smitten with the disease. An 

 interval of twenty- six years from the first observation of Davaine, was 

 closed by Koch's memorable investigation. 



Pasteur long held himself aloof from any direct examination of 

 the germ theory. But he must have been profoundly impressed 

 by his own experiments on silkworms, and he was at length made 

 aware of the vast promise of the field of inquiry which his own 

 researches and those of others had opened up. Attacking the subject 

 of splenic fever, he soon gave evidence of the genius which charac- 

 terised his former work. Take an illustration. Koch had proved that 

 while mice and guinea pigs were infallibly killed by Bacillus anthracis, 

 birds were able to defy it. Why ? Here is the answer given by Pasteur. 

 The higher limit of temperature which arrests the multiplication 

 of the bucillus in infusions is 44° Cent. (111° Eahr.) The tempera- 

 ture of the blood of birds is from 41° to 42^ Cent. It is therefore 



