304 BIOLOGY. [Book iv. 



Such puerilities- as these are surely far more difficult to admit 

 than the spontaneous formation of some very simple living* types 

 at the outset of the organic world, even though many observa- 

 tions and experiments do not plead very eloquently in favour 

 of spontaneous generation even at our epoch. Certain vegetal 

 parasites develop themselves- under the epidermis of living 

 plants. Whence can come the seeds of these entophytes which 

 appear even in plants destitute of stomata ? ^ Microscopic mush- 

 rooms spring up and live in the citrons. The forester Hartig 

 found some in the cavities of' the ligneous part of trees, under 

 numerous sound annual layers. Marklin has seen the white of 

 a hen's egg converted into sporotrichum. Very recently vibrions 

 were met with in the pus of a closed abscess. In his Histoire 

 des HelmintheSj M. Dujardin speaks of the rhdbditis aceti, which 

 dwells exclusively in wine ■finegar, and is found neither in the 

 vine nor in grapes. Whence then does it come ? And especially 

 where were its germs when man made neither wine nor vinegar ? 



The cause of generation, spontaneous, equivocal, heterogenical 

 has moreover never ceased to have partisans. No one has de- 

 fended it with more force, perseverance, and talent than F.-A. 

 Pouchet, from whom we now propose to borrow some arguments. 



Most of the organic macerations abandoned to themselves, at 

 a suitable temperature, at the end of a time which varies; but is 

 tolerably short, are peopled by vegetal and animal proto-organisms. 

 According to the adversaries of heterogenesis, these myriads of 

 new beings proceed from germs floating in the air. But' whoso 

 says germ saysovulum, that is to say, cell of a diameter perfectly 

 appreciable in the miscroscope, for the ovulum of certain ciliated 

 microzoa varies from 0™°0028 to 0'°",0420' in diameter; 



Now, if by the- aid. of the aeroscope of Pouchet, we examine 

 microscopically one cubic decimetre of air, by making it pass 

 through an orifice of a' quarter of millimetre of section, that is 

 to say by drawing it out to a length of 4^00 metres, it is only 



^ F.-A. Pouchet, N'ouvelles Experiences sur la Ohiiration Spontanie et shut la 

 SSsistance VitaU, p. 117. 



