uuexpocted. It was his aim to determiue the precise character of the 

 contagious matter which previous experiments had proved to be ca- 

 pable of indetinite transfer and reproduction. He examined the 

 diseased organs of mau and the lower animals microscopically, and 

 found the tubercles infested with a minute rod-like parasite which he 

 called Bacillus tuberculosis. These rods vary from one seven-thou- 

 sandth to one ten-thousandth of an iuch in length, and their diameter 

 is about one-tenth as much. Within these rod-like plants more or 

 less globular spores are formed, which, under favorable cu-cumslan- 

 ces, after the disintegration of the parent plant, will develop into new 

 plants. 



Koch first discovered this parasite by staining the thinnest possible 

 slices of the diseased tissues with methylene blue in alcohol, fol- 

 lowed by a solution of vesuvin. By this method the tissues are 

 slightly colored with brown, while the Bacillus stands out clearly of a 

 bright blue color. This method of staining has been improved upon 

 by Ehrlich, Baumgarten and others. These bacilli were separated 

 and cultivated on specially prepared blood-serum for more than six 

 months in some cases, and then these purified bacilli were inoculated 

 into healthy animals of various species, and in every case there was 

 a multiplication of the parasite and a reproduction of the original 

 disease. Since that time the greatest activity has prevailed in exper- 

 imentation ; and with new and improved methods, the conclusions 

 of Koch have been tested and verified again and again, till the facts 

 are now placed beyond all doubt. 



DISTRIBUTION OF TUBERCULOSIS. 



Tuberculosis occurs in cattle wherever they are kept in domestica- 

 tion, but seems to be most prevalent where consumption is most 

 common in the human family. It is almost unknown in Iceland, and 

 is very rare in Polar countries generally, but increases as we approach 

 warm climates. It appears to be very common in Italy and Algeria ; 

 and, according to Fleming, it is becoming more common in England. 

 I am not able to give any estimate of the prevalence of this disease 

 among the herds of Massachusetts, but my attention has been called 

 to it so frequently during the past two years, that I am inclined to 

 believe that the disease is more common than is generally supposed. 

 On two occasions I visited one of our large city meat marketS;, and 

 examined the lungs still attached to the livers offered for sale, and 



