. The principles of agriculture; a text-book for schools and rural societies . all this must be done within limitswhich will be compatible with the maintenance ofhealth and viaror. SrOGESTIOXS Oy chapter XIV 359rt. The best illustration which the pupil can secure of asingle-celled structureless organism is the amoeba (Fig. 84hThis lowly animal lives in stagnant pools, and can be secured\>y scraping the scum ofiE the stems and leaves of water plants,lu its larger forms it is barely visible to the naked eye. 3595. The Fig. 85 shows a spindle-shaped (involuntary) con-tractile cell or fiber fro
. The principles of agriculture; a text-book for schools and rural societies . all this must be done within limitswhich will be compatible with the maintenance ofhealth and viaror. SrOGESTIOXS Oy chapter XIV 359rt. The best illustration which the pupil can secure of asingle-celled structureless organism is the amoeba (Fig. 84hThis lowly animal lives in stagnant pools, and can be secured\>y scraping the scum ofiE the stems and leaves of water plants,lu its larger forms it is barely visible to the naked eye. 3595. The Fig. 85 shows a spindle-shaped (involuntary) con-tractile cell or fiber from the muscular layer of the intestine,showing nucleus in white and nucleolus in black. It has nosuch variety of functions as the amoeba has. 360a. A part or an organism is said to be specialized whenit is fitted for some particular work, rather than for general 232 THE PRINCIPLES OF AGRICULTURE work. A cell wtich has to do only with nutrition is special-ized ; one which has to do with nutrition, sensation, locomotion,and reproduction, is generalized. A ceD may be said to be. Rs. 84. Amoeba, showing large, rotuid niiclexLSnear the top, enclosing a niieleoliis, manygrannies, protruding arms of protoplasm. Pig. 85. and white spac-« ronnd which the proto- Muscle cell, plasm has flowed. Magnified 200 diameters. Magnified. still further specialized when it carries on some particular orspe^iial part of nutrition. 363a. A secretion is a material derived from the blood andpoured out into the body. When this material is of no furtheruse, it is eliminated, or removed from the body, and is known asan excretion. The saliva, eye-water, bile, gastric juice, are ex-amples of secretions. 363Z>. Glands are secreting organs. Thus the salivary glandssecrete or make the saliva or spittle, from the blood. Theliver is a gigantic gland, secreting bile and other materials. 364a. Glycogen is very like starch. In fact, it has the samechemical ;. It is rapidly changed into grapesugar
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