SECTIONAL TRANSACTIONS.— M. 413 



hospital ' is generally provided for sick or ailing pigs ; in this way the spread 

 of infectious or contagious disease is to a considerable extent controlled. 



Certain Scandinavian constructional points have been applied to pig 

 housing in England with satisfactory results. 



Pig recording was instituted in Sweden by the Pig Breeders' Society of 

 Malmohus to ascertain the productive capacity of sows. Records preserve 

 information regarding the number of pigs born and reared per litter, the 

 number and weight of the litter at three weeks old, their average weight, 

 variation in weight, their sex, and the number of teats of each female. 

 Three weeks is considered the best age at which to weigh to give a true 

 measure of the sow's milk yield. Records constitute the only reliable guide 

 to productive capacity and maternal qualities of sows. 



Large white sows at Moulton Farm Institute are now recorded on these 

 lines, and the figures obtained have demonstrated the importance and value 

 of recording. 



Careful selection of breeding sows according to records leads to a lowering 

 of the cost of production of pedigree breeding stock. 



Discussion. 



Afternoon. 



Discussion on The nature and importance of the clay fraction of soils 

 (Prof. G. W. Robinson ; Dr. C. E. Marshall ; Dr. R. K. 

 Schofield) : — 



Prof. G. W. Robinson. — Clay composition in relation to soil survey 

 and soil classification. 



The significance of the composition of the clay fraction depends upon 

 the extent to which it can be identified with the fraction of the soil resulting 

 from chemical weathering — i.e. the weathering complex. For most pur- 

 poses, the assumption of this identity does not involve a serious error. 



A broad distinction may be drawn betw^een clays with high and clays 

 with low SiOa/RzOg ratios. There is some justification for regarding a 

 SiOa/RzOa ratio of 2-0 as critical. Clay fractions with SiOj/RaOg ratios 

 greater than 2-0 occur under conditions in which removal of silicic acid is 

 inhibited by deficient leaching, as in arid soils ; by impeded leaching, as 

 in ground-water soils ; or by the protective effect of the calcium-ion, as in 

 carbonate soils. 



Clay fractions with Si02/R203 ratios of 2-0 or less are found under 

 conditions of free leaching, resulting in desaturation. Where leaching 

 takes place in the absence of acid humus, as in brown earths, red loams, and 

 red earths, the removal of silicic acid results, in soils of primary weathering, 

 in the formation of clay fractions with SiOj/RaOg ratios less than 2-0. 

 In the presence of acid humus there is a differentiation, owing to the 

 migration of sesquioxides from A to the B horizons. 



The study of the composition of the clay fraction may prove valuable in 

 the definition of soil series. 



Dr. C. E. Marshall. — The study of the clay particle. 



The accepted definition of clays on the basis of particle size involves the 

 soil worker in three interconnected groups of problems. First, there are 

 the purely physical problems, such as the extension of mechanical analysis 

 into the clay fraction itself. With this as starting-point the study of the 



