180 PEPPER TREE AS A CAUSE OF HAY FEVER. 



being earned further. As a matter of fact, in experiments 

 intended to ascertain the distance to which pepper tree pollen is 

 actually carried by the wind, it was found on plates suspended 

 1,000 yards (paces) from the nearest pepper tree. 



Thirdly : In iSloemfontein the pepper tree is grown as an 

 ornamental plant, both in gardens ancl on the streets, and in 

 many parts of the town is very plentiful. This will be apparent 

 from a table given in the next section, showing the results of 

 counting the number of trees on measured areas of the town. 

 Some 2,128 pepper trees were counted and the density was found 

 to vary from 1 tree per 449 square yards to 1 per 214 square 

 yards. The latter figure is fairly typical for areas of the town 

 where the tree is dense and is based on a count of 704 trees. 

 The circumstance that the pepper tree is so plentiful in many of 

 the residential parts of the town is a most important factor in 

 connection with the epidemics, and makes the case fundamentally 

 different from the usual one, where the plant producing the hay- 

 fever pollen is growing wild outside the town. It removes the 

 need for buoyant pollen and also explains why the pollen in 

 the air of the town was found to be so dense. For Dr. Scheppe- 

 grell has sho^wTi, by the exposure of pollen plates, that pollen 

 scatters rapidly as it is can-ied by wind from the parent .plant, 

 and that, roughly, the density of a pollen in the air varies 

 inversely as the square of the distance from the plant producing 

 the pollen. For example, at a distance of I'OO feet from a 

 source of pollen the amoimt of that pollen in the air would be, 

 roughly, 25 times as great as at a distance of 500 feet. Also, as 

 Dr. Scheppegrell has already shown, it is the density of a pollen 

 in the air which determines whether a patient shall suffer from 

 hay fever. Everyone can inhale a certain amount of pollen with- 

 out inconvenience, and suffering onh^ occurs when the amount 

 of pollen inhaled is in excess of the patient's neutralising power. 

 Hence arises the vital importance of proximity to a source of hay 

 fever pollen. 



XIII. Comparison of Bloemfontein with other Towns in 

 WHICH THE Pepper Tree Occurs. 



In Kimberley, as in Bloemfontein, the pepper tree has been 

 planted freely on the streets of the town, and there, too, 

 epidemics of hay fever occur when the tree is in flower, which is 

 about the same season as in Bloemfontein. On the other hand, 

 there are other towns in the Union, notably Grahamstown, 

 Maritzburg and Johannesburg, where pepper trees occur, which 

 are not troubled with serious hay fever when the tree is in 

 flower. The absence of hay fever from the three latter towns 

 would seem to cast doubt on the conclusion that the pepper tree 

 is the cause of the epidemics in Bloemfontein, and demands 

 investigation. The most probable explanations are, either that 

 the pollen does not find its way into the air of these towns, or if 

 it does so, then it is not in sufficient quantity to cause hay fever 

 to a serious extent. 



