
Some of these drugs have been and are used for the treatment 
against blackhead disease in turkeys and pheasants. Hinshaw 
et al. (1943) observed that soft-shelled eggs were produced in 
turkey hens within several hours after insertion of a single 
dose of sulfonilamide in the crop. The single dose capsule 
contained about 16 mg. of the drug. Adult White Leghorn females 
given single doses of 48 to 80 mg. sulfonilamide showed the 
same results. The effect of this drug on shell thickness was 
confirmed by Scott et al. (1944) by feeding at levels between 
0.5 and 0.002 per cent. 
b) The role of carbonic anhydrase and its inhibition by 
sulfonamides. 
Meldrum and Roughton (1933) were the first to advance 
the hypothesis that carbonic anhydrase might play a part in 
egg shell formation by influencing the rate of formation of the 
anion of calcium carbonate by catalysis of the reaction: 
CO2 + Ho0 -- Hatds 
It was shown by Keilin and Mann (1940) that compounds of the 
RSOONHs type (where R is a benzene, naphthalene or pyridine 
ring) specifically inhibit carbonic anhydrase in very small 
concentrations. This property is absent in such compounds in 
which the sulfonamide group is substituted: like sulfopyridine, 
and sulfathiozole. This was confirmed by Benesh et al. (1944) 
and by Bernard and Genest (1945). The latter, however, observed 
that by feeding sulfapyridine, there was a decrease in shell 
thickness varying between 19 and 25 per cent. Although the 
authors did not rule out the possibility that the drug could 
affect carbonic anhydrase, they suggested that the effect may be 
in inhibiting other enzyme systems associated with shell forma-~ 
tion. Gutowska and Mitchell (1945) observed that there is a 
relationship between the local concentration of carbonic anhydrase 
in the shell gland and the hen's ability to lay strong, smooth- 
shelled eggs. Carbonic Anhydrase acts as catalyst in the shell 
gland for the decomposition of carbonic acid, which may be formed 
from the bicarbonate ions in the blood, thus allowing a greater 
number of carbonate ions to be produced. Therefore, the enzyme 
dees not act in the formation of carbonic acid as suggested by 
Meldrum and Roughton (1933). 
The reaction: 2HCOz <-> HoC0z + COz 
The carbonate ions are then utilized in the formation of calcium 
carbonate, calcium being absorbed by the shell gland in its 
pound form (calcium proteinate) and dissociating it from the 
protein. Gutowska et ale (1945) inhibited the activity of 
27 
