1. The intestinal flora of Lucilia larvae consists mainly of non-lactose-fermenting, gram-negative bacilli which do not liquefy gelatine. Proteolytic organisms are not present in the gut in significant numbers, but they occur in blown meat.
2. A method of rearing larvae aseptically is described. The eggs are sterilised by treatment with 0.1 per cent, mercuric chloride solution and the larvae reared on heated brain mush, sterility being tested by inoculating aerobic and anaerobic media. The absence of symbionts transmitted inside the egg has been concluded from an examination of stained smears and sections of "sterile" larvae.
3. When larvae are reared aseptically on sterilised brain, the reaction of the gut contents is normal, tryptase is present in the intestine and excreta, and the growth rate is almost the same as in the presence of bacteria.
4. It is, therefore, concluded that micro-organisms play no part in intestinal digestion.
5. Sterile larvae excrete ammonia, but the amount is insufficient to make the food alkaline until the third or fourth day of larval growth. With infected cultures the reaction is distinctly alkaline on the second day.
6. The ammonifying bacilli isolated from normal larvae are probably responsible for the rapid appearance of ammonia in blown meat.