64 J. PERCY BAUMBERGER 



3. Preparation of medium, for microorganisms, i.e., leaf-cut- 

 ting ants, termites, ambrosia beetles. 



MICROORGANISMS AS LIQUEFIERS OF THE SUBSTRATUM 



The relation of the insect, microorganism, and substratum is 

 not always as clearly defined as in the preceding cases. Fabre 

 ('94) studied the food of LuciUa, the green-bottle fly, and came 

 to the conclusion that the larvae secrete a digestive fluid which 

 allows the liquefied albuminous material to be sucked up by 

 the insect. He placed in one tube of hard-boiled eggs a few fly 

 eggs and left the other tube of albumin equally exposed to the 

 air, as a check. The albumin on which the larvae emerged was 

 soon a liquescent mass, whereas the check dried up. Guyenot 

 ('07) reinvestigated the problem with Phoniiia regina Meigen and 

 also studied the anatomy of the larvae. The mouthparts as he 

 describes them are very similar to those of Drosophila larvae, as 

 mentioned above. The pharynx is immediately connected with 

 the crop of sucking stomach, a much distended flask-like struc- 

 ture which usually hes to one side of the oesophagus. Owing to 

 the nature of the pseudomaxillary apparatus, the larvae are un- 

 able to eat any solid food. Fabre had supposed the}' secreted 

 on the food some pepsin which liquefied the albumin. To test 

 this theory, Guyenot ground up the larvae and made various ex- 

 tracts. The extracts had no effect on starch, fat, or albumin; the 

 same was true of extracts of the salivary or gastric glands. The 

 normal liquefaction was then studied, and it was found that the 

 albumin was broken down to the peptone stage by a bacterium 

 Micrococcus fla^ois liquefaciens (Flugge) which was always pres- 

 ent with the larvae. The bacteria alone, without the acid of the 

 larvae had the same effect on the albumin, but at a much slower 

 fate. However, if they were mixed with the albumin with a 

 sterile platinum wire the speed was as great as with the larvae 

 present. As these bacteria were found in large quantities in the 

 sucking stomach of the larvae, Guyenot reached the following 

 conclusions : 



