THE DOCTRINE OF CONTAGIUM VIVUM. 325 



valuable as a triumphant demonstration of a disputed patho- 

 logical question, but is noteworthy as a model of patient, 

 ingenious, and most exact pathological research. 



We here come across an example of scientific prescience 

 on the part of two distinguished men which is worth notice. 

 It had been remarked by several observers that the conta- 

 gium of splenic fever, as it existed in the blood, was com- 

 paratively short-lived and fugitive, but that, under some 

 unexplained circumstances, the contagium was very per- 

 sistent, and lurked for years in stables and other places where 

 cattle were kept. Dr. Burdon Sanderson, writing in 1874, 

 inferred from this circumstance that the organisms of splenic 

 fever must have two states of existence ; namely, that of the 

 perishable bacteria found in the blood and some other more 

 permanent form, like seeds or spores, in which they were 

 capable of surviving for an indefinite period. In like manner. 

 Professor Cohn, guided by the botanical characters of the 

 rods found in the blood, classed them in that group of bac- 

 teria named by him Bacillus ; and, as he had observed that 

 all the Bacilli produced spores, he inferred that the Bacillus 

 anthracis, for so he named the bacterium of splenic fever, 

 would also be found to produce spores. These provisions 

 were proved by the researches of Koch to be perfectly exact. 



The following is a brief abstract of those points in these re- 

 searches which chiefly concern us. 



Koch found that mice were peculiarly susceptible to the 

 virus of splenic fever. The minutest particle of the fresh 

 blood or spleen of an infected animal infallibly produced the 

 disease when brought into contact with the living tissues of 

 the mouse. He found further that he could cultivate the 

 organisms artificially outside the body. He proceeded in the 

 following manner. He placed a speck of the spleen con- 

 taining the rods on a glass slide in a drop of the blood-serum 

 of the ox, or a drop of the aqueous humour of the eye of the 

 same animal, and covered it with a piece of thin glass. He 

 then placed the slide in an incubator maintained constantly 

 at the temperature of the body, and examined the prepara- 

 tion from time to time under the microscope. In a couple 

 of hours, he observed that the rods began to lengthen, and 

 in a few hours to grow into long threads. These threads, 

 after growing to twenty or a hundred times the length of the 

 original rods, began by and by to assume a dotted appear- 

 ance. The dots gradually increased in size and distinctness 

 until, after the lapse of fifteen or twenty hours from the 

 beginning of the experiment, they acquired the appearance 

 of strongly refractive oval bodies, which were placed at 



