BACTERIA IN DISEASE. 171 



The causes of these diseases have been very carefully sought 

 for by ordinary bacteriological methods with indecisive results. 

 Some of them no doubt are due to bacteria. In recent years 

 numerous observers have described a diplococcus or short 

 streptococcus as the cause of rheumatic fever or acute rheu- 

 matism. In the case of yellow -fever Sanarelli described an 

 organism (bacillus icteroides) as its cause, but his view is not 

 upheld by most of those who have worked on yellow fever.* 

 The bacillus described by a number of observers as having 

 been found in cases of whooping-cough may also be the cause 

 of that disease. f Bacilli have also been described in cases of 

 measles on several occasions. The organism obtained by 

 Lustgarten and that obtained by Joseph and Piorkowsky in the 

 lesions of syphilis are no longer regarded as the cause of the 

 disease, but the spirocheta pallida of Schaudinn and Hoff- 

 mann is probably the cause. 



It is likely that for some of the diseases mentioned other pro- 

 cedures than the usual methods of research will have to be 

 devised in order that the cause may be discovered. The proto- 

 zoa may play a part in the etiology of some of them. Roux has 

 produced evidence to show that contagious pleuropneumonia 

 of cattle is due to a microbe so minute that it is barely visible 

 with the highest powers of the microscope, so that its outlines 

 and its morphology cannot be studied. The virus of this 

 disease remains virulent after being passed through a Pasteur 

 filter, showing that it is small enough to go through its pores. 

 Similar experiments have succeeded with a number of other 

 affections of animals; for example, foot-and-mouth disease 

 and hog cholera or, at any rate, an infectious epidemic disease 

 presenting all the features of hog cholera. The virus may pass 

 thorugh a Pasteur or Berkefeld filter of a certain coarseness, but 



*Sanarelli. La Semaine Medicate. April, 4, 1900. Reed and Carroll. 

 Journal Experimental Medicine. Vol. V. 



fSee Czaplewski. Centralblatt }iir Bakteriologie. Bd. XXIV. 1898. p. 

 865. 



