42 THE JOURNAL OF BOTANY 



as the results were obtained by different methods. The method used 



originally by Danbar and extended by Cooke and Vander Veer, and 



again by Cooke, Flood, and Coca, was to prepare an extract of the 



poUen-proteid by means of grinding up the pollen (in the manner 



usual for enzjnue-abstraction) with sand, extracting the mass with 



distilled water by alternate freezing and thawing, or extracting with 



N 

 •8 7o NaCl in jttx NaOH. The product was precipitated by acetone, 



redissolved in -8 °/o NaCl, and standardized for nitrogen-content by 

 Kjeldahrs method. The toxicity was tested by applying the solution 

 at a known nitrogen-content to the conjunctiva, and by intradermal 

 injection. If the application produced lachrymation and sneezing, 

 and an itching weal at the point of injection, the result was positive, 

 and the subject considered sensitive to that particular pollen-protein. 

 The results obtained in this way are interpreted differently by the 

 different observers. Hay-fever is described : firstly, as due to a toxin 

 ("toxalbumin ") (Dunbar); secondl}^ as an anaphylactic reaction 

 (Cooke) ; and, thirdly, as a clinical symptomatic expression of local 

 spontaneous liypersensitiveness, the active pollen-substances not being 

 toxins (Cooke, Flood, Coca). These discordant results may perhaps 

 be explained as arising from the unnatural experimental conditions, 

 for under ordinary circumstances the nasal mucosa are not directly 

 placed in contact with poUen-proteid. There intervenes the highly 

 effective protective mechanism of the cuticularized microspore-wall. 

 It is true that in the Angiosperm pollens there are pores of 

 various kinds in the wall, but the mechanism by which colloidal 

 protein is to pass through a cellulose membrane is not explained. 

 The digestive power of the nasal mucosa is very slight, and in any 

 case there is no means of digesting cellulose there. The unbroken, 

 ungerminated pollen-grain is effectively sealed to protect its contents 

 from desiccation or undue wetting (in the case of wind-pollinated 

 forms like the grasses and Pinus), and conversely it is difficult to 

 understand how any of the protein -contents could passively diffuse 

 out. Possible germination-effects may also be set aside : even under 

 the most favourable circumstances grass-pollen does not germinate 

 within five minutes (?'. e, minimum "incubation-time" observed), and 

 in the case of G^minosperm-pollen the question does not arise. 



In the case of Angiosperm pollen, however, where the wall is 

 porose, the osmotic pressure of the grain (amounting to several atmos- 

 pheres) may be of importance, as leading to the withdrawal of water 

 from the adjacent membrane, with consequent swelling of the grain 

 and liberation of its contents through bursting. In this way the 

 alien protein would be brought into contact with the epithelial cells. 

 The irritation caused by the withdrawal of water by the grain must 

 also be quite considerable, having regard to the relative sizes of the 

 ciliated cells (6)u diam.) and pollen grains (30-50 m). Thus a single 

 80 /x grain of Finns excelsa would drain over a hundred epithelial 

 cells. 



It would be quite outside the scope of these notes to attempt to 

 deal with the question of protein-sensitization, which has been ex- 

 haustively treated in the papers already mentioned. Having discussed 



