TUBERCLE BACILLUS 207 



produced by it. But it was Koch who first discovered the 

 cause of the disease in the tubercle bacilli, recognisable in 

 all such products of the bodies of men and aaiimals as have 

 undergone tubercular changes. These furnish a foundation 

 for the doctrine that tuberculosis is transmissible, inasmuch 

 as Koch was able to set up a typical tuberculosis experi- 

 mentally in animals by means of pure cultures. Lortet 

 and Despeignes are of opinion that the tubercle bacilli 

 are frequently disseminated by earth-worms. 



Tubercle bacilli are fine rods having a length nearly equal 

 to the diameter of a human blood-corpuscle, somewhat 

 curved, and often united in groups of two or more, but 

 seldom in very extensive combinations. They are destitute 

 of motility. They form spores of an oval outline, both in 

 artificial cultures and in the bodies of animals, and offer 

 a high degree of resistance to drying, boiling, and the action 

 of the gastric juice and of putrefaction. The presence of 

 carbohydrates or of glycerine is, according to Hammer- 

 schlag, essential for their growth. 



The following is the procedure to be followed when it is 

 wished to obtain a pure culture of tubercle bacillus : — The 

 sputum of phthisical patients is mixed with water, and in- 

 jected into a subcutaneous sa,c made over the abdomen in 

 several guinea-pigs. In three or four weeks the tuber- 

 culosis will be so far advanced as to cause the death of one 

 or other of the animals, and in the post-mortem examina- 

 tidn tubercular changes will be found in the various organs, 

 particularly the omentum, spleen, and liver. Anothei- 

 of the animals is now killed by strangling, a window is 

 cut in the thoracic wall with all due precautions regarding 

 disinfection, and a corner of the lung drawn out with the 

 platinum wire. From this piece of lung some distinct 

 tubercular nodules are now taken and rubbed between two 

 slides. (Of course all the instruments used, such as knives, 

 scissors, and slides, must be carefully sterilised.) The 



