The Buffer Capacity of the Blood of the Sixth- Instar Southern Armyworm (prodenia Eri- Dania)^

It is well known that biochemical reactions take place in buffered media and that minor changes in hydrogen-ion concentration can affect profoundly the course of reactions. In the blood of man a variation of more than ±0.1 pH from the normal 7.4 is considered pathological, and a change greater than ±0.4 pH is usually fatal. The pH of the blood is maintained within these narrow limits by a system of buffers whose action is well understood. The buffer effect of the various constituents of the blood, as well as its buffer capo-city under both normal and pathological conditions, has been studied by Peters and Van Slyke {14Y and others. The blood of several marine invertebrates has also been found to be well buffered. Redfield et al. {16) summarized the early work in this field and showed that hemocyanin was the main buffer in the blood of Limulus polyphemus. The buffer capacity of the blood of only a few insects seems to have been investigated, but the blood of those studied is well buffered. The limits within which the pH of insect bood can range without resulting in the death of the insect appear not to have been determined. The variation from species to species and between individuals of the same species, however, is rather large. The pH of the blood of several species, as determined by Kocian and Spacek (iO), Bodine (4), Ludwig (ií), Babers (1), and others, varied between 6.0 and 7.3. Kocian and Spaéek found that in the same species the blood from individual insects might vary as much as 0.4 pH. The blood of Dytiscus marginalis L. was alkaline to litmus, according to Barratt and Arnold (2), and remained so when an equal volume of 0.03 N hydrochloric acid was added, but it became acid when an equal volume of 0.1 N acid was used. The same authors found the blood of Hydrophilus piceus (L.) to be alkaline to litmus but neutral when an equal volume of 0.025 N acid was added. Craig and Clark (7) titrated the blood of Pieris rapae L. and Heliothis armígera (Hbn.) {H, obsoleta (F.))^ with 0.1 N acid and alkali and determined the buffer capacity of the two bloods. These authors give the pH of the blood of P. rapae larvae as 7.17. This value is of interest because of the relative scarcity of reports of alkaline insect blood, and also because