THE ORIGIN AND PEOPAGATION OF DISEASE. 243 



of a spherical form, not more than j 5^00 of an inch in diameter. Tliey 

 belong to the genus Micrococcus, and those of the vaccine lymph are 

 designated by the name of Micrococcus vaccince. They increase in num- 

 bers if kept at the temperature of the living body, forming chains and 

 groups of associated articulations. Dr. Cohn finds similar bodies in 

 the fluid of small-pox vesicles, identical in size and appearance with 

 those of the vaccine lymph. " We must, therefore," he says, " for the 

 present regard the pock-lymph corpuscles as living and independent 

 organisms, belonging to the smallest and simplest of all liv^ing things, 

 which multiply, without formation of mycelium, by cell-division alone, 

 and perhaps also by tbe production of resting spores." 



Fiually, another kind of micrococcus has been described by Dr. Oertel,* 

 of Vienna, and by Prof. Ebert,t of Ziirich, as constantly present in cases 

 of diphtheria ; and both observers have found that its inoculation in dif- 

 ferent parts of the body in healthy animals produces a diphtheritic mal- 

 ady, having its starting-point at the place of inoculation. 



The contributions to medical literature on this subject have increased 

 of late with unusual rapidity. Since the beginning of 1870 more than 

 two hundred distinct publications have made their api3earance, either 

 in the medical journals, or as separate volumes, on septicsemia and 

 diphtheria, on micrococcus and bacteria, the ferment-corpuscles, ferment- 

 ation and putrefaction, their relation to contagion and infection, and 

 kindred topics. Many of these essays are extremely important, others 

 of more or less doubtful value. I have not attempted to notice them 

 all, but only those which seem to have really established some new facts 

 relating to the origin and propagation of disease. Should the discov- 

 eries of the next ten years continue to lead in the direction now indi- 

 cated, it will illustrate more fully than ever the intimate relation which 

 exists between all the branches of medicine and natural science ; for it 

 will show how large a part of human pathology is connected with the 

 general physiology of vegetative life. 



In connection with this subject a considerable degree of interest at- 

 taches to the ingenious experiments of Professor Tyndall on the dust- 

 particles suspended in the atmosphere. The fact that the atmosphere 

 is almost never free from floating molecules, diffused in greater or less 

 abundance by the air-currents, has for a long time attracted attention; 

 and it is a common observation that these dust-particles, even when in- 

 visible by diffused daylight, may at once be rendered evident by admit- 

 ting a sunbeam into a darkened apartment. The minute particles then 

 reflect the light, and become distinctly visible in the track of the beam 

 by contrast with the surrounding non-illuminated space. Professor 

 Tyndall, by passing the electric beam through a closed glass tube, has 

 shown that the atmospheric air, however transparent it may appear to 

 ordinary vision, is never so free from suspended particles that it will not 



* '• Deutsches Archiv f iir kliuisclie Medicin," 1871, B. viii, p. 242. 

 t "Zur Kentniss der bacteritisclien Mykosen," Leipzig, 1872. 



