﻿12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 59 



tal organisms ; but it arises among bacteria also. It persists in the 

 protozoal trypanosomes only as long as they continue to multiply 

 asexually in the blood of infected animals, and disappears as soon 

 as the normal state is reestablished, when the organisms multiply 

 sexually, as is their habit, in the body of insect parasites of the host, 

 as, for example, the rat-louse. Bacterial fastness, on the other hand, 

 tends to disappear when these parasites are cultivated artificially 

 outside the body. The particular significance of this resistant state 

 grows out of the circumstance that it is coming to be held account- 

 able for the troublesome or dangerous relapses that occur in many of 

 the infectious diseases. 



Manifestly the two factors of location and mutation will determine, 

 in no small degree, the effectiveness of the operation of specific 

 substances for treating disease. When the cause of disease is widely 

 disseminated in the blood, as in malaria, or when it is in the nature 

 of a chemical poison, as in diphtheria, it will obviously readily come 

 under the influence of the curative principles ; but when the infecting 

 microorganism takes up a position in the interior of a massive path- 

 ological formation, or in the crebrospinal membranes, for example, 

 the organism will be more difficult to reach and affect. By applying, 

 however, the specific therapeutic agent directly to the seat of the 

 disease, as is being done in the serum treatment of epidemic menin- 

 gitis, this obstacle to success is being removed. 



Bacteriology as a science may be reckoned as dating from the 

 overthrow of the spontaneous generationists and the discovery by 

 Pasteur of the cause of pebrine among silkworms. It was quickened 

 into active life and brought down to every-day use, and thus im- 

 measurably extended, by Koch. We are, as it were, still living within 

 the era of its first achievements, and thus we may reasonably hope 

 that this is merely the dawn of its beneficent triumphs. 



