348 
THE INFLUENCE OF THE H YDROGEN-ION CONCENTRA¬ 
TION IN THE DEVELOPMENT OF MOSQUITO LARVAE. 
(PRELIMINARY CONTRIBUTION.) 
By MALCOLM E. MacGREGOR. 
Wellcome Bureau of Scientific Research, Field Laboratory , Wisley , Surrey. 
It is a common experience that mosquito larvae when they are brought into 
a laboratory to undergo their development, often fail to develop normally. 
At times a high mortality takes place, or the larvae lapse into a condition of 
suspended development continuing as larvae for months. The latter phase 
usually ends in death before pupation can take place. I have been puzzled 
to account for these manifestations for a very long time, and have conducted 
various experiments in the hope of discovering the cause. The general opinion 
on the matter, I think, is that there is “something wrong with the food 
supply,” but as a matter of fact larvae supplied with an ample diet often 
show the same state of affairs. 
It appears that what underlies the phenomenon is not the fortuitous 
absence of certain food elements, but the influence that changes in the 
hydrogen-ion concentration have upon several factors in the larval develop¬ 
ment. 
In breeding the English tree-hole mosquitoes in this laboratory I found 
that the larvae, which were kept in the water from the tree-holes without the 
addition of other water, developed normally. It was at first thought that a 
high concentration of organic matter in the water was needed by the larvae, 
and therefore when dilution of the tree-hole water was necessary in order to 
increase the bulk, a generous supply of beech leaves taken from the tree- 
holes, and dead insects was added to this water. Tap water was used to 
dilute the tree-hole water. Nevertheless in every case the development of the 
larvae failed to continue normally. It was thought that possibly the tap 
water had some adverse influence, and filtered pond water was used subse¬ 
quently with no better result. 
Soon after an exhaustive series of experiments along these lines had failed 
to indicate w r hat underlay the phenomenon, it occurred to me to test the 
various waters in terms of the hydrogen-ion concentration. The local tap 
w r ater gave a P H of about 8, and all the waters of the local streams and 
ponds gave readings of P H 8*2 to 8*4 approximately. I then decided to test 
the tree-hole water and I v r as surprised to find that in every case alkalinity 
