CONCLUSION. 293 
situation is unfavourable to the life of the lower 
plants. 
The theory of microzyma explains the transmission 
of diseases by the organized elements of the virus, 
while the filtered liquid of the same virus is unin- 
jurious, and in this respect it is more in accordance 
with facts than the theory of blastema; but it does 
not explain the effect of the exclusion or sifting of 
the air by Guérin’s dressing, nor that of carbolic acid 
in Lister’s dressing. In fact, if the virulent microzyma 
are in the patient's body, and have no external source, 
it is difficult to understand of what use this process 
can be. It is evident that the cotton wool, which only 
arrests the solid particles of the air, while admitting 
the air itself, must act by warding off something 
suspended in the air, and the matter in suspension 
can only be organized bodies, or air-germs. 
Theory of Ptomaines—Special alkaloids (septine) 
were discovered by Panum in pus and by Selmi and 
Gautier in putrefying matter (ptomaines), and par- 
tizans of the theory of non-organized virus appeal to 
these as a last resource. It has been supposed that 
these ptomaines or toxic alkaloids were the product 
of putrefaction, or morbid changes which were purely 
chemical, produced in the tissues and fluids of the 
system, without any external intervention of microbes. 
This a priord idea does not really differ from Robin’s 
theory of blastema. If it is accepted, all pathogenic 
microbes resemble Sattler’s jequirity bacillus, which 
