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 Gue'rin'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 priori idea does not really differ from Robin's 

 theory of blastema. If it is accepted, all pathogenic 

 microbes resemble Battler's jequirity bacillus, which 



