26 <;KNKRAL HISTOLOGY. 



showed that when lime salts are slowly formed in organic col- 

 loids, as gum, albumen, etc., masses occur which are similar to 

 those formed in organized bodies. Thus they produced sphe- 

 roidal concretions of carbonate of lime, like some urinary de- 

 posits, discs like those of Bathybius, lamellae of shell substance, 

 and imitations of cuttlefish bone, etc. These experiments in- 

 dicate that calcareous and other deposits in tissues, as fish 

 scales, bone and teeth, may be accounted for by a vital modi- 

 fication of the ordinary forms of concretion. 



5. Reproduction. Parentage is the universal law of living 

 beings. Abiogenesis, or the spontaneous production of living 

 beings from non-living material, has been taught by some. 

 If animal or vegetable infusions are boiled in flasks and 

 hermetically sealed, infusorial organisms will after a time 

 be found in the flasks. This was considered evidence of 

 spontaneous generation, until it was shown that the germs 

 of infusoria existed either in the atmosphere or in the in- 

 fusion itself. Drs. Dallinger and Drysdale proved that 

 some germs resist a temperature of 300 F. Pasteur showed 

 that if the atmosphere is filtered by plugs of cotton wool 

 in the neck of the flasks, after boiling, the infusion re- 

 mained indefinitely free from infusoria, and Mr. Tyndall's 

 elaborate experiments respecting purified air tend to the same 

 conclusion. We may therefore regard the question of parent- 

 age as settled, and affirm, with Virchow, " Omnis ccllula c eel- 

 /;//<?" Every cell is from a cell. 



(1) Non-sexual parentage is seen in tissue bioplasts and in 

 the unicellular forms of animals and vegetables. It is a self- 

 division of the bioplasm, preceded by a vital movement and 

 division of the fibers of the nucleus. This self-division may 

 be a simple fission, a budding or protrusion and separation 

 of part of the mass, or an endogenous growth, which is a sort 

 of internal budding. 



(2) Sexual parentage is the union of a germ cell or ovum 

 with a sperm cell or spermatozoid, by which a new individual 

 is produced. In some species these cells are found in the 

 same individual, and in others the sexes are distinct. 



(3) In what is called alternation of generations the ovum 



