THE @SOPHAGUS, STOMACHS AND INTESTINES. 415 
But even if uric acid has been found in the Malpighian tubes 
of some insects, this does not prove their renal function, since 
the liver contains a large quantity of urea in mammals and of 
uric acid in birds. 
(5) ‘ The secretion of the Malpighian tubes agrees in no way 
with the hepatic secretion,’ 
Authors have repeatedly stated that the so-called bile tubes 
of invertebrates never contain the bile acids, and Griffiths 
[160] criticising my statements already published, says: ‘ It 
may be stated in passing that according to B. T. Lowne the 
Malpighian tubules of Calliphora Erythrocephala are ‘ hepatic ” 
in function. If by hepatic he means that these tubules have 
the function of a vertebrate liver, his conclusions are erroneous, 
for neither biliary acids nor glycogen are present in these 
tubules. Again, if he means by “hepatic,” they have a 
pancreatic function; this is also erroneous, because these 
tubules do not yield any digestive ferment or ferments’ 
(p- 96). 
These statements are sweeping, and would be serious if they 
were accurate. I cannot positively state that the Malpighian 
tubules of the Blow-fly or of its larva contain cholalic acid, but I 
can positively affirm that those of the larva give Pettenkofer’s 
reaction with great brilliancy, which is, to say the least, an in- 
dication, and a strong one, that they do contain cholalic acid 
or some closely-allied substance. On moistening a portion 
of the tubules with a weak solution of cane sugar, draining off 
the excess and treating with dilute sulphuric acid, draining 
off the excess again and heating carefully to dryness, they 
become an intense cherry red, and the above is the most 
delicate test I know for the presence of cholalic acid. 
I am quite aware that Pettenkofer’s reaction is unfortunately 
not distinctive of cholalic acid, and that it occurs in the 
presence of proteids and other organic substances, thus the 
fat bodies and even the blood of the larva give a brick-red 
reaction with this test; but, as Halliburton states,* no organic 
* *Text-book of Chemical Physiology,” London and New York, 1891, 
p. 682. 
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