354 Dr Eschricht's Inquiries concerning 



laws as those of other living beings, modifications, as usual, 

 existing according to the particular wants of each animal. 

 3. That a chief character of parasitic life is its concealment, 

 escaping the attention of those who are its victims. Every pa- 

 rasitic animal is the offspring of that provident mother Nature, 

 and, as much care is taken for the preservation of a disgusting 

 tape-worm as for that of a higher organism. Unprovided, 

 apparently, with organs of sense, or even with a brain, and ex- 

 tremely slow in its motions, it finds means of securing itself 

 and its young : whilst the human understanding is unable to 

 imagine what these means are, or declares it impossible that 

 any such should exist. 



Sect. 2. Jnfusory Animalcules compared with Entozaa. The 

 general remarks concerning infusoria were found applicable 

 also to the Entozoa. Again, what has been stated concern- 

 ing the Entozoa and their relation to the bodies they in- 

 fest, may be applied to the infusoria and their relation to the 

 terrestrial world. If we are correct in maintaining that the 

 inquiry as to the mode in which these animals propagate and 

 acquire a footing in their extraordinary habitats, demands a 

 particular answer for each separate species, which is to be an- 

 swered in each case only by a long and laborious investigation, 

 the remark is equally applicable to the infusory animalcules, 

 whose different species select some pure cold water, others 

 acid or salt fluids, and others hot mineral springs ; and to in- 

 fusory plants, of which particular species seem to be associated 

 with every variety of fermentation, as observed by Dr Schwann 

 and M. Caignard-Latour. 



Sect. 3. The two opposite Theories cotnpared in relation to 

 Experimental Physiology/, — To suppose that ova and seeds are 

 antecedent to animals and plants, wherever they appear, is 

 considered by the defenders of spontaneous generation as con- 

 trary to the genius of experimental physiology ; and there might 

 be some truth in the reflection, if the hypothesis necessarily 

 induced an indifference which was satisfied with this explana- 

 tion ; but it is useless, as well as untrue, when it only adds a 

 spur to the discovery of the occult phenomena connected with 

 their curious history. On the other hand, the theory of equi- 

 vocal goneratiou may appear favourable to experimental phy. 



