358 SECTIONAL TRANSACTIONS.—A™, B. 
is then outlined. "The mathematical method for the determination of the 
contribution of the Coulomb forces to the elements of the frequency 
equation is dealt with first; and the question of the contribution of the 
“repulsive forces’ is then considered. 
The results of a determination of the frequency spectrum for some of 
the alkali halides are then described ; and the results are compared with 
those obtained from crystal models. The positions of the subsidiary 
maxima in the absorption spectra of the alkali halides are deduced according 
to the theory of Born and Blackman. 
A determination of the frequency spectrum for a strained crystal lattice 
and a consequent investigation of the conditions under which the vibrations 
of the ions become unstable, lead to a new treatment of the problem of the 
breaking of crystals under stress. 
SECTION B.—CHEMISTRY. 
Thursday, September 5. 
PRESIDENTIAL ADDRESS by Prof. W. N. Haworty, F.R.S., on The molecular 
structure of carbohydrates (10.0). (See p. 31.) 
Dr. W. T. J. Morcan.—The function of polysaccharides in immunological 
specificity (11.0). 
The recognition of the important part played by polysaccharide sub- 
stances in the specific serological reactions that take place between virulent ~ 
forms of bacteria and the homologous antibacterial immune serum followed 
the discovery that filtrates from rapidly growing pneumococcus cultures 
contain a soluble product which gives specific precipitation with the homo- 
logous immune serum. Subsequently the serologically reactive material 
was identified as a complex polysaccharide which had been derived from 
the bacterial capsule. ‘The capsular substance, which is different for each 
kind of bacterium, is responsible for the specific serological reactions of the 
organism with its homologous antibacterial immune-body. 
Experiments with synthetic carbohydrate-protein antigens indicate that 
the ultimate specificity that is characteristic of bacterial polysaccharides 
depends upon (1) the stereochemical arrangement and the chemical nature 
of the groups attached to the terminal carbon atom of each hexose molecule, 
(2) the position of the linkages that join the hexoses together, and (3) the 
configuration of the hydroxyl groups of the hexoses that exist within the 
polysaccharide complex. 
Evidence has recently been obtained that the specific groupings which 
are associated with the serological activity of the group specific substance of 
horse saliva, the blood-group substance A of man and the specific hapten 
of the heterophile or ‘ Forssman ’ antigen are polysaccharide in nature. 
Dr. E. L. Hirst, F.R.S.—Optical activity and structure of sugars (11.25). 
The numerous empirical rules by which attempts have been made to 
correlate structure with optical rotatory power in the sugar group are valid 
only within narrow limits. For example, if the lactones of sugar acids 
and their methylated derivatives followed invariably an extension of 
