1877.] 



the Germinal Particles of Bacteria. 



419 



which the existence of structure is inferred the following may be 

 mentioned : — The protoplasm of a Ehizopod is admitted to have structure 

 because, although none can be seen in the protoplasm itself, the complicated 

 form of the calcareous shell which the protoplasm makes or models can be 

 seen. By analogy, therefore, other organisms which are allied to the Ehizo- 

 pod are inferred to have structure ; and from these, or from similar cases, 

 the inference is extended to all kinds of cells, with respect to which it is 

 taught by physiologists that although, in certain cases, no parts can be dis- 

 tinguished, the living material of which they consist is nevertheless endowed 

 with structure or organization. Similarly we assume that a Bacterium pos- 

 sesses a more complicated structure than we can actually observe, because 

 in other organisms which are allied to it by form and life history such 

 complications can be seen. Again, in all embryonal organs we admit 

 the existence of structure before it can be seen, because in the course of 

 development we observe its gradual emergence. So far inference of the 

 existence of structure from historical evidence is justifiable ; but if we 

 were to carry this inference back to the ovum itself, and say that the 

 characteristic structures of nerve, of muscle, or of gland exist in the 

 ovum at the moment after impregnation, every physiologist would feel 

 the assertion to be absurd. 



In the familiar comparison of the origin of the elephant with that of the 

 mouse, in which the perfect anatomical similarity of the ova in the two 

 species is contrasted with the enormous difference of the result, we should 

 be justified in saying that the difference of development is the expression 

 of structural difference between the primordium of the one and the primor- 

 dium of the other ; but inasmuch as it is not possible to indicate any 

 anatomical distinction, it is understood that structural difference of 

 another kind is meant, namely, difference of molecular constitution. In 

 other words, we assume that the potential difference between the one 

 and the other is dependent on an actual difference of molecular structure. 

 "Whether this is accompanied with an anatomical difference, such as we 

 might expect to be able to see if we had more perfect instruments, we 

 do not know. 



Prom the moment that it is understood that the word structure means 

 anatomical structure, the argument used by Dr. Tyndall loses its 

 relevance. After referring to the " germ-limit," he says, " Some of those 

 particles " (by which, I presume, is meant atmospheric particles) " de- 

 velop into globular Bacteria, some into rod-shaped Bacteria, some into 

 long flexile filaments, some into impetuously moving organisms, and some 

 into organisms without motion. One particle will emerge as a Bacillus 

 antliracis, which produces deadly splenic fever; another will develop 

 into a Bacterium the spores of which are not to be microscopically dis- 

 tinguished from those of the former organism; and yet these undis- 

 tinguishable spores are absolutely powerless to produce the disorder 

 which Bacillus anthracis never fails to produce. It is not to be imagined 



