IMMUNITY AGAINST MICROBES. 425 



day hardly any bacilli are found at the seat of inoculation. 

 On the fifth day the few bacilli which can still be seen are con- 

 tained in migrating cells, and show evident signs of the most 

 advanced degeneration. 



The study of the initial lesion of animals in which a chronic 

 form of the disease has been induced by the inoculation of large 

 quantities of a weak virus (0*40 centigramme or more) is not 

 less interesting. 



The animals inoculated with a strong virus perish so soon 

 after the introduction, that the struggle between the cells and 

 the micro-organisms is more or less one-sided ; for although 

 the animal dies, most of the cells present at the point of 

 inoculation are normal and show no signs of degeneration. 

 When, however, a chronic form of the disease is produced, 

 many of the lymphocytes perish as the result of their struggle 

 with the invading bacilli. 



If the animal dies on the fourth or fifth day, sections through 

 the exact spot where the virus has been inoculated show that 

 the bacilli have infiltrated the neighbouring muscles to a far 

 greater extent than in the acute form of the disease. Many 

 bacilli are extra-cellular, lie in a coagulated inflammatory 

 effusion, and are perfectly normal and healthy, staining well 

 with aniline dyes, and retaining colouring matters in a normal 

 fashion. A few micro-organisms are contained within amoeboid 

 cells, and often present various forms of degeneration; but 

 although in the acute form of the disease most of the wander- 

 ing cells are healthy, many of the cells met with in the more 

 chronic affection are markedly degenerated. In other words, 

 they become true pus-cells — that is, dead cells. 



The nucleus of such a cell, instead of staining deeply with 

 carmine or logwood, possessing a coarse intra-nuclear network, 

 and being marked off sharply from the surrounding protoplasm, 

 stains rather more diffusely, and often shows signs of breaking 

 up. In later stages the nucleus undergoes distinct fragmenta- 

 tion, three or four fragments of nuclei lying in the protoplasm 

 of a cell. In the last stage the nucleus disappears, nothing 

 remaining but a pale round mass of protoplasm, which no 



