1888.] Mr Stewart on Decomposition of Proteid Stibstances. 401 
proteids and non-proteid bodies, and especially between proteid s and 
inorganic salts, be able to initiate changes which may lead to the 
absorption of considerable tissue masses. 
I hope before long to be able to complete this piece of work, and 
to bring it into relation with some investigations which I have 
begun on the changes produced in various tissues, especially muscle 
by the passage of strong currents, a subject for information upon 
which gynecology is at present looking to physiology. 
It does not need to be pointed out that the questions as to how 
much of the conduction in muscle and nerve is electrolytic conduction 
and what are the electrolytes, are intimately connected with the 
whole subject of electrical stimulation. 
6. On the Malpighian Tubules of Lihelhda depressa. 
By Dr A. B. Griffiths, F.K.S. (Edin.), F.C.S. (Bond, and 
Paris), Principal and Lecturer on Chemistry and Biology, 
School of Science, Lincoln; Member of the Physico-Chemical 
Society of St Petersburg, ^'c. 
In this memoir details are given which prove the true renal 
functions of the Malpighian tubules in the Libellulidge. 
Libellula depressa (the dragon-fly) is a voracious insect, which 
lives in water during its earlier stages, where it undergoes an 
imperfect metamorphosis, the pupa finally creeping out of the water 
and giving birth to the perfect insect. By experimenting with a 
large number of the larval forms of Libellula, the author has 
extracted (from the larvae) uric acid crystals, by using similar 
methods to those described in his papers already published in the 
Proceedings of the Royal Society of Edinburgh (vol. xiv.). Of course 
it is difficult to say whether the Malpighian tubules are developed to 
any degree of perfection in the aquatic larvae of the Libellulidae ; 
for the secretion of urinary products (uric acid, &c.) is capable of 
being produced in other organs besides the true invertebrate kidney. 
The author has shown, in a paper about to be published, that the 
stomach of Uraster rubens performs a double function.* It is a di- 
gestive gland and also an excretory organ, separating the nitrogenous 
products of the waste of the tissues, &c., from the blood in the form 
of uric acid, which is to be found in the five pouches of that organ. 
* Proc. Roy. Soc. Land., vol. xliv. pp. 325-328. 
