122 JOURNAL OF THE [November, 



acted upon the blood as to enable it to resist the effects of the 

 Bacillus tuberculosis — possibly, by driving the organism into 

 recesses where it could do no harm. 



In the study of bacteria a well-made microscope is essential — 

 one having an accurately moving stage and a good substage con- 

 denser. The objectives should be a ith and jsth of the first 

 quality. Staining fluids are used, some for coloring the organ- 

 isms and some for coloring the tissues containing them. A good 

 way of studying them without staining is as follows : Put a drop 

 of gelatine on a cover glass, touch the gelatine with the bacteria, 

 and then place the cover, prepared surface under, over the de- 

 pression in a hollow-centred slide. By this means their devel- 

 opment can easily be watched. Much, however, is required be- 

 sides mere observation of occasional individuals under the 

 microscope. They must be studied in large quantities. Pas- 

 teur's method involved the use of liquid media, such as soup, 

 bouillon, milk, and various chemical fluids. While much valu- 

 able work was done by this method, accurate results are more 

 easily reached by the use of solid media, in which the German 

 investigators are proficient. Potatoes and fruits were first made 

 use of for this purpose. I have here to-night, on potatoes, speci- 

 mens of Micrococcus prodigiosus. In one specimen the growth is 

 in the shape of the letters C. F. C. The bacteria were planted 

 yesterday. The Micrococcus prodigiosus has been the cause of 

 considerable discussion. Its presence in bread gave rise in 

 former times, to wonder and fear, and its mysterious appearance, 

 as a blood-red I. H. S. on the holy wafers, through the agency 

 of some shrewd priests, was looked upon by many devout lay- 

 men as miraculous. In preparing these media, care must be 

 used to destroy such bacteria as may be already present. From 

 a potato, the bad spots, also the " eyes," must be removed. Then 

 the remainder should be placed for an hour or two in a bath of, 

 say, corrosive sublimate. Next, it should be put into a steam 

 sterilizer under which a flame keeps the water boiling furiously, 

 forcing the steam through the grating, and cooking the potato 

 resting upon it. The potato is then put into a moist chamber 

 previously sterilized, and is therefore protected from atmos- 

 pheric germs by coverings of filter paper kept saturated with the 

 sublimate solution. The hand and the implements used in the 

 operation should also be sterilized. To inoculate the potato, 



