232 BACTERIA. 



tained bacilli or spores), and by a process of close siege pre- 

 venting the organisms from making their way outwards, and 

 confining them entirely to their own territory, so that, 

 when they have utilized what food material there is in the 

 degenerated cells, they are no longer able to exist as vege- 

 tative bacteria, and only the spores remain which may, 

 however, remain latent for a very long period awaiting a 

 favourable opportunity for another attack on weakened 

 tissues. These spores or hibernating germs are confined 

 within the same area, and the debris with its contained 

 spores is gradually encroached upon by the surrounding 

 tissues until, eventually, if the mass is not large it may be 

 entirely absorbed, though, owing to the amount of fibrous 

 tissue that is formed by the attacking cells after their activity 

 is somewhat diminished, this process of absorption sometimes 

 goes on very slowly. 



It was an easy enough matter, when the history of the 

 development of the tubercle bacillus was known, to kill the 

 organism outside the body, and Koch found that a very large 

 number of germicidal substances were capable of interfering 

 with its growth ; but unfortunately most of these germicides 

 also exerted an injurious effect on the tissues, so that what 

 was gained in one direction was lost in another. 



In most other diseases in which preventive or curative 



inoculation by means of vaccines less virulent cultures of 



the microbes to accustom the animal to the action of the 



poison and so enable it to resist the more virulent, has been 



\ attempted, the aim has been to render the bacilli less, and the 



vf cells more active, and to develop in these cells a special activity. 



By accident, as he tells us, Koch found that by injecting 

 tubercle virus into the subcutaneous tissues of guinea- 

 pigs which had been previously inoculated with tuberculosis, 

 the tissue in which the tubercle bacilli were acting was 

 actually destroyed and an eschar or slough was formed 

 at the point of inoculation ; whilst although the bacilli 

 were not directly destroyed, they remained embedded 

 in a mass of food material that was gradually but surely 

 used up to supply the needs of these bacilli, and 

 eventually they had to go into winter quarters. But 

 the products of the tubercle bacilli appear to act in 

 some way on the tubercles already formed ; they do 

 something more than bring about complete degenera- 



