Dr. Griffith on the Sacculi of the Polygastrica, 179 



rate interpretation I attributed to him was rather my own, I crave 

 the favom* of a few hnes to reply. In the first place be it noticed, 

 that the quoted remarks relating to this part of the subject in my 

 paper were extracted (as distinctly stated) from the ' Prov. Med. 

 JournaP for 1842, as read before the British Association ; there- 

 fore obseiTations since made in any ^Experimental Researches' 

 published in the following year, clearly can have nothing to do 

 with the matter. It must also be observed, that my observations 

 were on the Polygastrica, not on ParamcEciurrif although what ap- 

 plies to one will, 1 believe, apply to the whole. 



My object in adducing "physical reasoning '^ was not to at- 

 tempt to show what any living structure could or could not do, 

 because 1 appealed to experiment and observation first, and sub- 

 sequently applied reasoning to explain what I saw ; the explana- 

 tion of the causes of which appearances must be sought in reason- 

 ing alone. 



As regards the bursting of pollen grains when acted on by 

 solution of potassa, this is again a decided misinterpretation, and 

 the cause of this appearance is only to be found in repeated ex- 

 periment and careful reasoning. When water, solution of potash, 

 or acid are added to pollen grains, imbibition and swelling take 

 place ; when water, acid, or weak potash water are used, the pollen 

 tubes are generally thrust out at the same time, and the fovillary 

 matter can be seen within ; but when a stronger solution of pot- 

 ash is added immediately as the pollen tube begins to be emitted, 

 it is deprived of its covering of intine by the solvent action of the 

 reagent, and the fovillary particles are emitted, thus giving the 

 appearance, which, hastily interpreted, is called bursting. The 

 physical reasoning is therefore equally cogent as regards the 

 pollen and the animalcules. The '' vesicular" appearance seen in 

 the animalcules after the addition of potash can also be seen in 

 the case of the pollen, and when the solution is not sufficiently 

 strong to dissolve the intine covering of the pollen tube, the whole 

 grain shrinks or becomes contracted. When we neutralize the 

 liq. potassse exactly with nitric acid previously to adding it to 

 the Polygastrica (whereby the solvent action of the liquid is de- 

 stroyed, but its density not materially interfered with), we have 

 exosmosis produced, i, e. instead of swelling they become con- 

 tracted and shrivelled. This is a very interesting fact, and clearly 

 shows that the density of the liquid cannot be concerned in the 

 production of the "imbibition," but that it must be attributed 

 solely to the chemical action of the potash. 1 may here recall 

 to the reader^ s mind, in conclusion, the object I had in making 

 any observations relative to the " imbibition" which was stated 

 to take place in the poly gastric sacculi, — it was to disprove the 

 conclusion arrived at by Mr. Addison, viz. that these " stomachs" 



