162 RECENT RESEARCHES 



practical observers, the Bacillus has invariably been found in con- 

 firmed cases of Phthisis, whereas in ordinary Bronchitis the search 

 has always been in vain. Dr. G. A. Heron, who has been paying 

 special attention to this subject, considers that the numbers and 

 forms in which the Bacilli are found in the expectoration of con- 

 sumptive patients, is likely to be of great use in forming an opinion 

 as to the probable gravity of the disease. That where, in the early 

 history of a case, they are few in number, it will probably run a 

 long course ; but that if, on the contrary, the Bacilli are persistently 

 numerous and grouped in considerable masses, it will run a short 

 course, and rapidly end in death. 



The power of modification of the potency of Bacteria, as agents 

 of disease, also throws much light upon many of the phenomena of 

 Zymotic diseases. It opens up the possibility of affording pro- 

 tection against all diseases which are caused by Bacteria^ by atten- 

 uating the virulence of such disease germs by successive cultivation, 

 and then by inoculation causing a mild attack of the disease which 

 shall be protective against severe attacks. This, as we have seen, 

 has been practically carried out in the case of Chicken Cholera 

 and Anthrax. The statistics for the department of the Eure-et-Loire 

 in France, for last year, have shown that in inoculated flocks of 

 sheep, the mortality has been reduced to one quarter of what it 

 would formerly have been, while among inoculated cows and oxen 

 it has been reduced from 7-03 to '24 per cent. 



The modification of other organisms by their " environment " 

 may also help us in considering the modifications of the Bacteria. 

 We know that many of our most valuable plants and fruits are 

 " cultured " varieties of useless and semi-poisonous vegetables, and 

 we see that many fungi produce transitional form, according to the 

 host on which they are developed. Thus the common wheat 

 mildew {Fuccijiia grami?iis), if sown on young berberry plants, pro- 

 duces the ^cidium Berberidis ; while the ^cidium spores sown 

 on young wheat produces the Uredo^ which is the first stage of 

 Wheat mildew, each form being confined to the special plant on 

 which it is produced. So with the salmon-disease. Dead flies are 

 often seen in the autumn sticking on the window-panes, their bodies 

 covered with fine white powder, and the same substance adhering to 

 the glass beneath and around them. These dead flies have been 



