298 THE WONDER OF LIFE 



are able to feed upon oxalic acid, and perhaps other organic 

 acids, produced by the Fungus. But after we allow for 

 these and other complications, there remains no doubt 

 that many lichens illustrate a very effective symbiosis 

 or mutually beneficial partnership of a Fungus and an 

 Alga. 



A very interesting three-fold association has been in- 

 vestigated by Prof. Bottomley. Nitrogen-fixing Bacteria 

 (Azotobacter and Pseudomonas) are found along with Blue- 

 Green Algae (Nostoc and Anabcena) in the thallus of the 

 liverwort Anthoceros and in the leaves of Azolla, the Water 

 Fern. The same combination of Bacteria and Algae is 

 found in the roots of Cycas. It may be that the Alga 

 supplies the necessary carbohydrate for the Bacteria, 

 and that the host-plant profits by the nitrogen-fixing 

 powers of the Bacteria. 



It is usual to find numerous Bacteria living in close 

 association with animals in the food-canal, in the mouth, 

 in the lungs, in the tissues, and some experts have raised 

 the question whether a higher animal could live a normal 

 life without its internal flora. By ingenious carefulness 

 M. Michel Cohendy, working at the Pasteur Institute, 

 has been able to rear chicks to an age of forty-five days 

 without their showing any trace of microbes. At that 

 date they became too big for their antiseptic cage and had 

 to be let out quite healthy and vigorous. In about 

 twenty-four hours those that were tested had the usual 

 stock of microbes. As they stood the sudden infection 

 quite well, it is plain that the power of resistance to ordinary 

 microbes is inborn or constitutional, not an individual 

 acquisition. 



Just as there are friendly Bacteria in many animals, 



