MICROPHYTES FOUND IN THE BLOOD. 367 



plained on Davaine's supposition that the organisms, retaining 

 their vitality for a long time in dry air, were conveyed by air 

 currents, or that inoculation was effected by insects, and so forth. 

 Koch's experiments lead him to believe that Davaine's explana- 

 tion of the mode of propagation of the disease is only partially 

 correct. He found that bacteridia-staves were not so hardy as 

 Davaine had supposed. Blood which contains only rods will 

 retain its property in the dry state for but a few weeks, and 

 when moist only for a few days. How, therefore, could the 

 contagion remain dormant in the soil for months and years ? If 

 bacteridia had anything to do with the matter, it must be 

 assumed that during some stages of their development they were 

 inert, or that, as Cohn had suggested,^ resting spores were formed 

 which had the power of retaining their vitality for a long time, 

 and of giving rise anew to bacteridia. The existence of such 

 spores is what Dr. Koch beheves he has been able to demonstrate. 

 As this question is a very important one, it is necessary that the 

 evidence adduced should be submitted to careful examination. 



The experiments of Davaine and others were repeated, mice 

 having been found to furnish the most satisfactory results. The 

 tail was seized, and a small portion of its skin being abraded, 

 a drop of the fluid containing the bacilli was placed in contact 

 with the small wound. Such inoculations proved to be invaria- 

 bly fatal when fresh material was used. In order partly to 

 ascertain whether the bacilli passed into some other form 

 by successive inoculations, and also to provide himself with a 

 constant supply of fresh material, he inoculated one mouse after 

 another, the last mouse supplying the material for its successor, 

 until eventually a series of twenty inoculations had been con- 

 ducted ; consequently twenty crops of bacilli had been cultivated 

 without any marked change in their character being noticeable.^ 

 The pathological results were always of the same character — en- 

 larged spleen, and motionless, translucent bacilli (fig. 3). The 

 latter in mice were more numerous in the spleen than in the 

 blood, but different animals showed different results as regards 

 their distribution in the tissues — the blood of inoculated rabbits, 

 for example, being often so free from them as to be traced with 

 difficulty, though the spleen and glands contained plenty, 

 whereas in guinea-pigs the number of bacilli in the blood was 

 often so great as to equal, if not exceed, that of the red blood- 

 corpuscles. 



On adding a little of the spleen affected with bacilli to per- 

 fectly fresh aqueous humour and subjecting the preparation to a 

 temperature of 35-37° C. for from 15 to 20 hours, the bacilli 



> Cohn's ' Beitrage,' Band i, Heft. 3. 



2 Davaine bad conducted a similar series of inoculations. 



