236 



NUTRITION 



the muscular labor keeps up the heat-production, and by urging a rapid 

 flow of lymph all over the body, sustains the metabolic furnace at its 

 limit of vigorous action. Contrast physiologically with these conditions 

 those of the city business-man who rides from his home to his office in 

 heated vehicles, takes no exercise, worries more or less, and who has 

 in consequence a poor digestion. This man has no need of increasing 

 heat-production by eating much, for his metabolic fire, low and dull 



FIG. 129 



The common so-called bear-animalcule (Macrobiotus Hufelandi), a tartigrade, in its active and 

 in its dried (hibernating) states. (Greef and Plate.) As seen under the microscope in the latter 

 condition it is not to be distinguished from a speck of quartz. In this state the animal will remain 

 months or even years, yet on addition of water, it will within an hour or two oftentimes resume its 

 complex animal activities. This, then, is the extreme protoplasmic type of hibernation common 

 to bears, hedgehogs, bats, gophers, woodchucks, etc., and voluntarily attained for purposes of gain 

 by certain human fakirs of India. Eating no food, the temperature falls from 5 to 13 C., the 

 heart slows and weakens its beat, respiration is greatly lessened, and the whole metabolism is re- 

 duced to a minimum. For the two to six months that hibernation lasts, the homotherm becomes 

 practically a poikilotherm. In the case of mammals, actual drying of the protoplasm does not, 

 of course, occur, but in both alike the two vital physical principles, heat and moisture, are 

 lessened. These are the conditions of movement, and movement in turn is the physical basis of 

 life. The bear of the forests and the bear-animalcule of the eaves-troughs of our houses alike, 

 then, lower their metabolism for purposes of self-preservation during inevitable long periods of 

 severe environmental stress which else would kill them. 



as it is, supplies all needs. But physiologically speaking these are two 

 distinct planes of living, if perfect metabolism be a just criterion. It is 

 easy to increase heat-production, much easier than to lessen it, for the 

 combustion in the tissues cannot be checked. If fuel, therefore, be not 

 supplied them from without, they will consume themselves. As is well 

 known, a rise of temperature usually increases chemical action, so that 



