MICROBES IN THE HUMAN BODY 31 



microbes. But the recent polar expeditions failed to find a 

 single animal of this kind. 



Nevertheless, such have been found among the burrowing 

 larvae which excavate galleries in the thickness of leaves and 

 live shut off from the external world by a transparent wall of 

 epidermal cells. The truth of this can be demonstrated by 

 extracting them with a sterile needle through a litttle perforation 

 made in the epidermis after sterilisation with peroxide of hydro- 

 gen. According to Portier's experiments, the Lithocolktis 

 caterpillars are aseptic in about a third of the cases ; those of 

 the Nepticula of rose-trees always. These burrowing larvae 

 dispose of their excreta by stowing them aseptically in their 

 closed tunnels, whereas Zischeria, which discharges its dejections 

 externally, through a little hole made in the leaf, is always 

 contaminated. 



Finding experiments on these small invertebrates easy, 

 Bogdanoff introduced the previously disinfected eggs of flies 

 into sterile meat and found that the larvae hatched and kept 

 under these conditions develop less well than the control larvae 

 fed on putrefying meat rich in bacteria. When he added to 

 the sterile breeding ground a digestive ferment capable of 

 attacking meat, i e. y trypsin, the sterile larvae flourished equally 

 with the others. Bogdanoff would have concluded that the 

 bacteria play the necessary part which in the latter case was 

 performed by the ferment, had he not found some sterile broods, 

 without addition of ferment, quite as vigorous as in ordinary 

 breeding. Larvae can thus develop w ithout the aid of microbes. 

 Wollmann using an excellent technique has finally proved this : 

 he succeeded in breeding from the egg sterile flies. " During 

 the first days of life the sterile larvae develop more slowly than 

 the contaminated controls, probably because the digestive 

 glands are not yet in full activity and find the sterilised meat 

 difficult to attack. Later these differences disappear and the 

 sterile larvae attain the weight and size of normal adults." 



Experiments on aseptic breeding of vertebrates, such as 

 Pasteur desired, have been carried out, with a patience 

 worthy of all praise, by Nuttall and Thierfelder, who took young 



