Pathogenesis, Immunization. 35 



gation of the bipolar Ijacilli. Through the destruction of the 

 tissues by the other organisms the entrance and propagation 

 of the ovoid bacteria are favored. 



Their invasion is without doubt of a secondary character 

 in those cases in which a general septic affection is caused by 

 an ultravisible virus, as for instance in dog distemper and hog 

 cholera (see those diseases). In these affections disease proc- 

 esses may develop subsequently which are exclusively or at 

 least partly the result of the action of the ovoid bacteria. In 

 recognition of this fact, the etiological importance of these bac- 

 teria has already been considerably limited. 



Immunization. Pasteur proved that cultures of the chicken 

 cholera organism when attenuated by keeping in the air pro- 

 duce a suitable vaccine for the immunization of chickens against 

 artificial infection. Similar results are obtained with cultures 

 attenuated by higher temperature or by disinfectants. How- 

 ever, the results of such immunizations which are mostly limited 

 to laboratory experiments are by no means uniform. This 

 irregularity is probal)ly due, on the one hand, to the variance 

 of the virulence of the cultivated l)acteria, and on the other 

 hand, to the difference of action of the methods employed in 

 the attenuations, accurate control of which is almost impossible. 



More recently J. and M. Lignieres (1902) produced a potent vaccine for all the 

 diseases of this group from cultures which had been reinoculated several hundred 

 times from agar to agar at two days' intervals, as a result of which they possessed a 

 uniform virulence. Flasks with a wide bottom are tilled to a height of ^2 cm- 

 with peptone-bouillon and inoculated with the stock culture. The tla?ks are then 

 placed in a thermostat and kept at a temperature of 42-43° C. The cultures 

 which are grown for five days at this temperature produce the first, while those 

 grown only for two days, the second vaccine. 



With the attenuated cultures immunity may be produced 

 not only against the same variety but also against related 

 varieties of the bipolar bacillus. Kitt was the first to point out 

 the possibility of a uniform procedure for the control of the 

 diseases of this group. He successfully immunized chickens 

 against fowl cholera with the virus of rabbit septicemia. Later 

 Jensen obtained the same results w^tli the virus of infectious 

 pneumonia of calves. Lignieres also proved that this reci- 

 procity obtains with regard to all strains of the varieties of 

 bacteria belonging to this group. He succeeded in demonstrat- 

 ing experimentally that a vaccine prepared from a culture of 

 a certain variety is potent in the first place against this variety, 

 but that it also has a protective action, although of a lesser 

 degree, against the bipolar organism of the other diseases of 

 this group. But its protective action for the latter diseases is 

 so slight and uncertain that it does not meet with practical 

 requirements, and besides the preparation of the different vac- 

 cines for each of the diseases would be very troublesome. 

 Lignieres therefore prepared a so-called polj^v^alent vaccine 



