THE CAUSE OF TUBERCULAR DISEASE. 257 



magnetism, magnetic interference, etc. He has been able to trace out 

 the direction of the lines of force produced in the liquid with the ap- 

 paratus represented in Fig. 2. A light sphere or cylinder is mounted 

 in the midst of the liquid upon an elastic rod, so that it shall partake 

 * of every movement of the surrounding water ; a brush is attached to 

 it, and arranged in such a manner as to paint, on the glass plate above, 

 the line of every vibration of the fluid important enough to move it. 

 If two drums are used pulsating concordantly, a figure is obtained 

 precisely like that produced by iron filings in a field of two similar 

 magnetic poles. If the pulsations are discordant, the figure is like 

 that obtained with two dissimilar poles. Three pulsating drums give 

 a figure identical with that produced by three magnetic poles. 



A number of interesting conclusions may be drawn from these ex- 

 periments concerning the nature of electric and magnetic vibrations, 

 but they need to be further confirmed before a positive announcement 

 of them can be justified. 



-*-~o~ 



THE CAUSE OF TUBERCULAR DISEASE. 



LETTER FEOM PEOFESSOE TYNDALL TO THE LONDON "TIMES." 



ON the 24th of March, 1882, an address of very serious public im- 

 port was delivered by Dr. Koch before the Physiological Society 

 of Berlin. It touches a question in which we are all at present in- 

 terested that of experimental physiology and I may, therefore, be 

 permitted to give some account of it in the " Times." The address, a 

 copy of which has been courteously sent to me by its author, is en- 

 titled " The Etiology of Tubercular Disease." Koch first made him- 

 self known by the penetration, skill, and thoroughness of his researches 

 on the contagium of splenic fever. By a process of inoculation and 

 infection he traced this terrible parasite through all its stages of de- 

 velopment and through its various modes of action. This masterly 

 investigation caused the young physician to be transferred from a 

 modest country practice, in the neighborhood of Breslau, to the post 

 of Government Adviser in the Imperial Health Department of Berlin. 

 From this department has lately issued a most important series of 

 investigations on the etiology of infective disorders. Koch's last in- 

 quiry deals with a disease which, in point of mortality, stands at the 

 head of them all. If, he says, the seriousness of a malady be measured 

 by the number of its victims, then the most dreaded pests which have 

 hitherto ravaged the world plague and cholera included must stand 

 far behind the one now under consideration. Koch makes the start- 

 ling statement that one seventh of the deaths of the human race are 

 due to tubercular 4isease, while fully one third of those who die in 



VOL. XXI. 1*7 



