TEXT-BOOK OF BACTERIOLOGY. 



233 



artificially-coagulated blood-serum could be used which he (Koch) 

 introduced for this very purpose. 



Substances containing bacilh were spread on such coagulated, 

 transparent blood-serum and left in an incubator at 37° C. The 

 repeated examination with low magnifying powers resulted, after 

 several days, in the discovery of peculiarly-shaped colonies consist- 

 ing only of tubercle bacilli, as ascertained by stronger magnification 

 and the color reaction. 



It may be thought that there is nothing easier than estabUshing 

 pure cultures of bacilli according to the method prescribed. But 

 whoever undertakes It and finds out by his own experience the ex- 

 traordinary difficulties that must be contended against, will admire 

 again the success of Koch, who obtained entirely by his own efforts 

 all the data which we follow to-day. 



Pure cultures, according to Koch, are obtained as follows : 



Inject into the abdominal cavity of some animals— for instance, 

 the very susceptible Guinea-pigs— some tuberculous poisonous mat- 

 ter, such as consumptives" sputum ground and washed with distilled 

 water. After some time, about three to four weeks, the first of the 

 inoculated animals will die and the post-mortem will show an exten- 

 sive tuberculosis of the liver, spleen, lungs, etc. Now one of the 

 remaining pigs is killed by strangling and immediately cut open, 

 before putrefaction bacteria or some other foreign micro-organism 

 can settle, in order to obtain available inoculating matter. The 

 skin is turned back with sterilized instruments, a window is cut 

 into the chest-wall, and the root of a lung is drawn out with a 

 platinum wire. (Knives and scissors must be free from germs.) 

 Take from the organ one or more distinct nodules and place them 

 upon glass slides thoroughly steriUzed. The tubercles should be 

 firmly crushed between the latter and the bacilli thus exposed as 

 much as possible. 



Blood -serum cannot be spread on plates. Allow the fluid serum 

 to coagulate in small glass cups, and distribute the crushed tuber- 

 cles on the surface of this firm nourishing medium with a strong 

 platinum loop as forcibly as possible; it is best to rub the inoculat- 

 ing matter directly into the blood-serum. The little cups are then 

 carefully covered with glass plates and placed in the incubator. 



It is difficult to understand why, in spite of all precaution, the 

 separation of germs in this manner is not as thorough as by the 

 method with the plate. Stress must for this reason be laid upon a 

 careful removal of the matter. We must also bear in mind that 

 the tubercle bacillus possesses extremely little energy of growth, 

 thrives very slowly, and develops exclusively at breeding tempera- 



