6 HISTORICAL INTRODUCTION. 



Diybys Theory. 



Some fifty years later an extremely interesting book 

 was published bearing the following title : ' A Dis- 

 course concerning the Vegetation of Plants, spoken 

 by Sir Kenelm Digby, at Gresham College, on the 

 23d of January 1660. (At a meeting of the Society 

 for promoting Philosophical Knowledge by Experi- 

 ments. London : Printed for John Williams, in Little 

 Britain, over against St Botolph's Church, 1669.) ' 

 The author attributes plant-growth to the influence 

 of a lalsam which the air contains. This book is 

 especially interesting as containing the earliest rec- 

 ognition of the value of saltpetre as a manure. The 

 following is an extract from this interesting old 

 work : 



" The sickness, and at last the death of a plant, 

 in its natural course, proceeds from the want of that 

 balsam ick saline juice ; which, I have said, mak'es it 

 swell, germinate, and augment itself. This want may 

 proceed either from a destitution of it in the place 

 where the plant grows, as when it is in a barren soil 

 or bad air, or from a defect in the plant itself, that 

 hath not vigour sufficient to attract it, though it be 

 within the sphere of it ; as when the root has become 



asserted that he had himself witnessed the fact, and, as -an interest- 

 ing and corroborative detail, he added that the mice were born full- 

 grown. See 'Louis Pasteur: His Life and Labours.' By his Son- 

 in-law. Translated by Lady Claud Hamilton. (Longmans, Green, 

 & Co.) P. 89. 



