2l8 ESSENTIALS OF BACTERIOLOGY 



there. It has been found in the brain, spleen, liver, and 

 kidneys. In the secretions it has not been discovered. 



Agglutinating substances have been developed. Immu- 

 nity has been produced in rats, and the serum has anti- 

 toxic properties. 



Transmission. The bedbug retains the spirillum in its 

 blood and is considered an important factor in spreading the 

 disease. 



African Tick Fever. A spirochaete similar to that of 

 relapsing fever has been observed in ticks, which conveyed 

 a disease to monkeys similar to the above fever. 



CHAPTER XXIX 

 FILTERABLE ORGANISMS 



Filterable or Ultra-microscopic Organisms. There are 

 many widely distributed infectious diseases that have all 

 the characteristics of germ or bacterial diseases, but so far 

 the organism has not been found. It has been suggested 

 that the bacteria are so small that they pass through the 

 ordinary germ-filters and are beyond the powers of the 

 microscope. By aid of the ultra-microscope twice the mag- 

 nification of the usual oil-immersion lens can be obtained, 

 and it is hoped that the cause of some of these diseases will 

 thereby be ascertained. The instrument is still imperfect, 

 though even so it has opened up a new field of research. 



Such diseases as measles, foot and mouth disease of cattle, 

 typhus fever, small-pox, scarlatina, and infantile poliomyeli- 

 tis (epidemic infantile paralysis) are assumed to be due to 

 these bacteria. 



Small-pox and Vaccinia. The exciting agent of small- 

 pox is still unknown, but numerous bacteria and protozoon- 

 like bodies have been described and given etiologic signifi- 



