656 TRANSACTIONS OF SECTION f. 
tions in retinal qualities then may explain both the horizontal-vertical illusion 
itself and the difference found between the two eyes, for the retina of one eye 
may be somewhat different in this respect from the other. Practice was found 
to result in an increase of the illusion, whereas psychological illusions have 
almost invariably been found to decrease with practice. ‘This increase seems 
connected with the assumption by the subjects of a more confident ‘ mechanical ’ 
attitude in making their judgments, basing them more and more on immediate 
sensory data. 
6. The Guanidine Group in the Protein Molecule. 
By Professor A. KosseEt. 
We may assume, as is well known, the following linkage of amido-acid within 
the protein molecule :— 
“ee Ai pie eer Twinn Hc finan Bela ae 
R Ry Ra 
In the process of hydrolysis, with the entry of water the carbohydrate chain 
is detached at the positions indicated by the dotted lines, and amido-acids are 
formed. 
NH,—CH—COOH cha a a ae ee 
| 
R Ry Rg 
Proceeding from this basis, and working with the simplest proteins—namely, 
the protamines—I have endeavoured to determine the position of arginin and 
lysin in the protein molecule. Both of these amido-acids contain two amido- 
groups, and therefore for each of them there are two combining possibilities, 
according to whether one or both peptid links take part. These are repre- 
sented in the following formule for lysin in A, and A,, for arginin in B, 
and B,. The investigations, which have been carried out in association with 
Messrs. A. T. Cameron, E. L. Kennaway, and N. Gawrilow, proved that the 
formule A, and B, represent the combining conditions. 
The proofs rest chiefly on the characteristic properties of the guanidine group 
of the arginin molecule. This group determines alkaline reaction, but under 
the conditions defined by Van Slyke gives no reaction with nitrous acid and 
contains no nitrogen capable of titration by the Sérensen method. 
...NH‘CH:CO... ...NH‘CH-CO... 
du, ‘NH, ba, ‘NH-CO‘CH-NH, 
bo. sg COxx 
(A,) (Ad) 
...NH‘CH‘CO... ..NH‘CH‘CO... 
C,H, C,H, 
bn Ne 
dsc dyn 
tu, tH-co ‘CH—NH, 
(By) (By) 
hv 
