346 



themselves, not one of which, however, may be developed 

 into an ordinary yeast cell,"^ except it meet witli an appro- 

 priate medinm, Avhen its further development is accomplished, 

 terminating in the formation of a fungus with aerial fructifi- 

 cation. 2 



The argument that we may dispense with pre-existent 

 oerms in the case of monads and bacteria because we do not 

 suppose them in the formation of crystals, of course derives 

 its force from the assumed identity of the modes in which 

 the matter of either is built up. But even a bacterium is 

 something very different from an aggregation of its lifeless 

 constituent matter. The minutest crystals, on^ the other 

 hand, differ in no respect from the largest except in size, and 

 give as definite angles and measurements ; their shape, in 

 fact, is implicitly determined by that of their constituent 

 molecules, to which it must be simply related. These mole- 

 cules can be separated by solution and reaggregated again 

 without limit, always with the production of identical crys- 

 talline forms. It cannot be imagined, however, that bacte- 

 rium elements pre-existed in a solution ready to come toge- 

 ther into a bacterium ; nor is there any reason to suppose 

 that the particles of a bacterium are capable of nndergoing 

 separation with the subsequent reconstitution of the bacte- 

 rium form like a crystal. And even supposing that this Avere 

 possible it would only show that a bacterium was very differ- 

 ent from other living things. Moreover.if a bacterium under- 

 went such a disintegration the fragments would be nothing 

 more than " germs," and would almost certainly reproduce 

 bacteria, not by coalescing, but severally, by growth at the 

 expense of surrounding nutritive matters ; and if they did not 

 do this it is difficult to see how they could aggregate into 

 anything more than an amorphous mass. 



To Pasteur belongs the credit of having demonstrated the 

 existence of germs and spores in the air, and the method by 

 which he achieved this is well known. It was not, perhaps, 

 perfectly adapted to demonstrate their existence optically, as 

 the minuter particles of living matter could hardly fail to be 

 altered if not destroyed by the treatment with different liquids 

 necessitated by the process, even if they were visible to the 

 low powers which were used. According to Dr. Hughes 



1 ' Disease Germs,' p. 20. 



2 By a curious coincidence, ou the next pag;e following the first instal- 

 ment of Dr. Bastian's memoir, is an abstract of a paper by Dr. Polotebnow, 

 " On the Origin and Development of Bacteria." He finds an unbroken 

 series of forms between the minute round cells which form the mycelium of 

 FemcUlium, and probably other fungi and fuUy-developed Bacteria, which 

 he thinks can oulv occur from these cells.— (Zee. clt., p. 178.) 



