A very pernicious delusion is prevalent, that children ought to be “hardened” to the influences of cold, and that too much clothing “makes them tender.” Excessive clothing may possibly increase the tendency to “catch cold,” owing to its exciting perspiration, or owing to the fact that the extra clothing is commonly thrown off at irregular intervals—witness the effects of wearing a scarf round the neck occasionally. But to suppose that children can be hardened by exposure of arms and legs, and other parts of their bodies, is irrational. A large amount of heat is lost from these bare surfaces, and apart altogether from the danger of chill, more food must be taken to compensate for this loss of heat, and keep up an equable temperature. Also if the food taken is expended in preserving the warmth of the unprotected body, less material is left for the purpose of growth. From these causes it frequently happens that children remain stunted in growth, even if latent disease is not actually developed by the extra strain on their resources. The children of the very poor are often pointed to as demonstrating the power of hardening. It is forgotten how many of these poor children have perished under the hardening system, and that the good health of those remaining is in spite of the hardening. =Poisonous Dyes in Clothing.=—These, like poisonous wall-papers, were formerly much more common than at present, and, as in wall-papers, the poisonous agent has most frequently been arsenic, large quantities of which were formerly used in the preparation of certain dyes. Occasionally such poisonous pigments are still employed. The means of detecting arsenic in any fabric or wall-paper are given on page 216. CHAPTER XLI. PARASITES. =Parasites= (Greek, _para_, upon, and _siteo_, I feed), in the broadest sense of the word, are living organisms, which derive their nourishment from other living organisms. They may belong to the vegetable or animal kingdoms, and may live on the skin, in the alimentary canal, or in some one of the internal organs. Some, like the fungus causing ringworm, feed on the living tissues of the animal infested; others, like tape-worms, on the partly digested food; while other parasites, like fleas, only pay temporary visits to the surface of the body, for the purpose of obtaining food. =Vegetable Parasites.=—Vegetable parasites all belong to the class of fungi, and more accurately to the two lowest divisions of this class which have been provisionally formed, viz.—Schizophyta, and Zygophyta. The Schizophyta include two orders, =Schizomycetes= and Saccharomycetes. BACTERIA.