BY R. GREIG-SMITH. 



735 



ing point, they were reduced only to 667 ; and, when boiled for an 

 hour, they increased to three and one-quarter millions. 



Extracts of the garden-soil at various depths were made, in order 

 to see to what extent the toxins had been washed down by previous 

 rains, and instead of subjecting the extracts to 100°, the lower tem- 

 perature of 60° was employed. The top inch of the soil was re- 

 moved, and the succeeding three-inch portions were taken. The 

 two lower layers contained some clay, which had probably been 

 put there when the sandy soil had been used as a garden, about 

 twenty years ago. 



Experiment xii. 



The first and second three inches, which, together, may be taken 

 as representing the soil, have much the same nutritive power, and 

 have much the same behaviour. The third three inches, which may 

 be taken as the subsoil, is much less nutritive. The toxin is appar- 

 ently different, for heat, at 60°, does not increase the nutritive 

 effect. It does not appear that the soil-toxin has been retained by 

 the subsoil, unless it is that the rain of the previous three days 

 had been excessive. On the 28th, 29th, and 30th June, the soil 

 received 3, 25, and 71, points of rain, respectively, that is, a total 

 of, practically, an inch of rain upon the three days preceding that 

 on which the soil was taken. The conditions were, therefore, 

 against finding toxin in the soil. There appears to be an increase 

 of toxicity upon heating the extracts of the subsoil at 60°, or, what 

 may be the equivalent in this case, a diminution of nutritive effect, 

 which does not occur in toxic soils. The portions of soil were cut 

 out with a circular tin-cylinder of 3-5 inches diameter, and three 

 inches deep. Each portion weighed approximately 400 grams. The 



