1910.] 



The Origin of Osmotic Effects. 



593 



This conclusion is in harmony with that to be drawn from Vinson's recent 

 observations on " The Stimulation of Premature Ripening by Chemical 

 Means," the account of which [published in the February number of tlie 

 ' Journal of the American Chemical Society ' (vol. 32, p. 208)], reached us only 

 when we had practically completed our experiments. Vinson's work relates to 

 the ripening of seedling dates by exposure to various vapours or in solutions. 

 He has tried over 100 substances. Those which he finds to be effective, with 

 very few exceptions, are such as we should suppose would be active. He 

 concludes that the apparent stimulation of ripening depends solely on the 

 killing of the protoplasm — that " in broad terms, any substance which will 

 penetrate the cuticle and kill or stimulate the protoplasm, thereby releasing 

 the previously insoluble intracellular enzymes without rendering them 

 inactive, will bring about ripening, provided the fruits have reached a 

 certain necessary degree of maturity." 



The differential septum of the leaf appears to be even more delicately 

 discriminative than is that of the barley grain. 



Since Graham's classical researches on diffusion, it has been customary to 

 distinguish two classes of substances — colloids and crystalloids ; it now 

 appears to be desirable to divide the latter broadly into two sub-classes 

 according as they will or will not pass through differential septa such as are 

 met with in the barley grain and the laurel leaf. Starling has proposed to 

 apply the term " Hormones " (from 6p/xdco, I excite or arouse) to the 

 chemical messengers, which speed from cell to cell along the blood stream 

 and co-ordinate the activities and growth of different parts of the body ;* and 

 he has already ranked carbon dioxide among the hormones. It appears to us 

 desirable to apply the term to all substances which pass through membranes 

 such as we have referred to and excite activity within the cell. 



As in the case of the barley grain, the entry of the diffusing substance into 

 the leaf appears to condition the more or less rapid entry of water ; the 

 substance^ which exercise this influence, in both, cases, are substances which 

 have but slight attraction for water. In other words, the hormones are 

 " anhydrophilic " substances ; hydrophilic substances generally fail to 

 penetrate differential septa which are selective to the degree manifest 

 in cereal grains and the laurel leaf. 



It is a most striking fact that substances usually considered to have little, 

 if any, chemical activity should be the most active in initiating enzymic 

 change in the leaf, e.g. toluene, carbon bisulphide, chloroform and ethereal 



* The Croonian Lectures, on the chemical correlation of the functions of the body, 

 delivered before the Eoyal College of Surgeons, June, 1905. — ' The Lancet.' 



