PHYSIOLOGICAL 281 



More than ten thousand termites of two different species were used 

 in the experiments, and they grew and multipHed for eighteen 

 months without the sHghtest sign of malnutrition. Growth and 

 multipHcation occurred with the same rapidity as in the controls 

 that received their normal diet of wood. Some of the colonies that 

 were started with ten adults had after eighteen months more than 

 two hundred half-grown individuals. The weight had increased 

 forty times on a diet of filter-paper ! 



Many herbivores feed mainly on carbohydrates, such as sugar, 

 but that is very different from a diet of pure cellulose. There are 

 many extras in the herbivore's diet of grass or clover. Yet the 

 herbivores do utilise much cellulose, and in doing so they seem to 

 be indispensably helped by Bacteria and Infusorians in their food- 

 canal. It is therefore interesting to notice that all the wood-eating 

 Termites that have been examined contain an abundance of intes- 

 tinal Infusorians (of remarkable beauty, like those of a horse's 

 stomach), which have been proved to help in the utilisation of the 

 dry-as-dust food. Similarly, in many wood-eating insects, like the 

 larval death-watch or bookworm, there are partner yeast-plants 

 which seem to have a fermentative action on the contents of the 

 food-canal. Many cases are now known of this kind of vital partner- 

 ship or symbiosis, but we should like to hear more about growing 

 fat on filter-paper. 



OTHER EVERYDAY FUNCTIONS 



CIRCULATION OF THE BLOOD.— What should everyone 

 understand in regard to the circulation of the blood? The use of 

 the blood in an ordinary backboned animal is fivefold, (i) It dis- 

 tributes through the body the digested food by which the living 

 tissues are kept in repair and by which the engines of the body, 

 the muscles, are kept able to continue contracting. (2) It carries 

 the oxygen quickly from the place of capture, say the lungs, to 

 the place of combustion, say, the muscles; and it likewise carries 

 the carbonic acid gas from the place of formation, say, the muscles, 

 to the place of liberation, say, the lungs. (3) With the help of the 

 lymph, which bathes the tissues very intimately, the blood collects 

 the soluble nitrogenous waste, and takes it to the filters — notably 

 the kidneys — by which it is excreted. This fine nitrogenous waste 

 is partly due to the wear and tear of the living tissues and partly 

 to the unused residue of digested nitrogenous food distributed by 

 the blood. (4) From the ductless glands, or organs of internal 

 secretion, such as the thyroid gland and the suprarenal bodies, 

 the blood carries away certain potent chemical messengers or 

 hormones which are distributed throughout the body, regulating 



